1 Introduction

Throughout the twentieth century, states were at the center of global governance. International regimes and formal intergovernmental organizations (FIGOs) were the dominant vehicles for cooperation among nations (Krasner 1983; Keohane 1984; Abbott and Snidal 1998). Centralization, hierarchy, and formalization through interstate treaties were the hallmarks of international institutions, such as the United Nations (UN), International Monetary Fund (IMF), World Trade Organization (WTO), and European Union (EU) (Abbott et al. 2000; Koremenos et al. 2001).

Yet, beginning in the 1980s and accelerating in the 1990s, states have increasingly turned to governance through informal intergovernmental organizations (IIGOs) (Vabulas and Snidal 2013, forthcoming) and transnational public-private governance initiatives (TGIs) (Abbott and Snidal 2009; Westerwinter 2021), among other institutional forms, to structure their interactions and to govern cross-border problems. IIGOs are organizations in which states meet regularly to make policy and coordinate behavior without a formal secretariat or institutional structure (Vabulas and Snidal 2013). Examples include the various G groups (e.g. G8 or G20) (Gstöhl 2007; Cooper and Pouliot 2015) and the Proliferation Security Initiative (Eilstrup-Sangiovanni 2009). In TGIs, by contrast, states work together with business actors and non-profit non-governmental organizations (NGOs) to govern problems that no actor alone has the knowledge, resources, or legitimacy to address effectively (Abbott and Snidal 2009). Examples include the World Commission on Dams (Dingwerth 2007) and the International Code of Conduct for Private Security Service Providers’ Association (Avant 2016).

Despite the recent surge in informal cooperation in world politics, research has largely focused on formal institutions, such as FIGOs and international treaties (Abbott and Snidal 1998; Goldstein et al. 2000; Koremenos et al. 2001; Barnett and Finnemore 2004; Hawkins et al. 2006; Koremenos 2016).Footnote 1 FIGOs and treaties are, however, only part of the complex patchwork of contemporary global governance (Lake 2010; Barnett et al. 2016; Kahler 2018). A sole focus on these institutional forms often provides inadequate, if not entirely misleading, descriptions of the games that actors play in world politics (Achen 2006; McKeown 2009; Stone 2013; Kleine 2013). For example, the rules of the game played in the WTO depart substantially from its formal treaty provisions (Steinberg 2002). Likewise, in the EU, the legislative co-decision procedure between the European Parliament and the Council of Ministers consists of an ensemble of formal and informal procedures that interact with one another in multiple ways to shape the interactions of member states and EU institutions (Farrell and Héritier 2003).

As these examples indicate, while formal rules are important features of global governance, in many situations, informal practices may override, substitute, or complement formal provisions. As a result, contemporary global governance can often not be fully understood by examining formal institutional structures alone. Understanding how world politics actually works requires a focus on informal governance.

Recent work in political science, economics, and international law has accordingly begun to examine informal governance as a mode of international cooperation (Stone 2011, 2013; Christiansen and Neuhold 2012; Pauwelyn et al. 2012; Kilby 2013; Kleine 2013; Hardt 2014), producing a rapidly growing number of studies in the social sciences (see Fig. 1).

Fig. 1
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Informal governance in the social sciences, 1980–2018

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In the broadest sense, informal governance refers to any rules, norms, and institutional structures and procedures that are not enshrined in formally constituted organizations or in their constitutions. Informal governance can be based on a variety of configurations of public and private actors ranging from purely intergovernmental cooperation to public-private arrangements to instances of governance that rely primarily on private actors. In this special issue, we focus on informal governance that involves states as one or the only type of participant. Examples include informal intergovernmental organizations, such as the G8 (Vabulas and Snidal 2013); transnational public-private governance initiatives of states, business, and NGOs, such as the Kimberley Process (Haufler 2010); and international customary law (Verdier and Voeten 2015).

Existing work largely focuses on informal governance within FIGOs (Steinberg 2002; Prantl 2005; McKeown 2009; Stone 2011; Kilby 2013; Kleine 2013; Vreeland and Dreher 2014; Hardt 2014, 2018), but the phenomenon is broader than this. Informal governance outside FIGOs is an important alternative to formal governance structures, and the two influence each other in diverse ways (Keohane and Nye 1974; Abbott and Snidal 2000; Raustiala 2002; Kahler and Lake 2009; Abbott et al. 2015; Andonova 2017; Abbott et al. 2018; Fioretos 2019; Westerwinter 2020). For example, states may prefer to cooperate using informal agreements because informality increases flexibility and speed, and reduces contracting costs relative to formal treaties and organizations (Aust 1986; Downs and Rocke 1987; Lipson 1991; Abbott and Snidal 2000; Prantl 2005; Sauer 2019; Abbott and Faude forthcoming). Furthermore, informal governance outside formal organizations can be a deliberate strategy of both strong and weak players, which seek to bypass unfavorable formal structures and enhance their bargaining positions (Vabulas and Snidal 2013; Avant and Westerwinter 2016). Informal cooperation can also be a strategic instrument to explore cooperative endeavors in relatively empty institutional spaces or to create new cooperative arrangements in densely institutionalized settings (Abbott et al. 2016; Westerwinter 2020).

In sum, while scholarship that focuses on formal intergovernmental organizations often neglects informal forms of cooperation altogether, work on informal governance within FIGOs tends to overlook informal governance outside formal arrangements. Both research programs can benefit from incorporating IIGOs, TGIs, and other informal governance modes into their models. Moreover, neglecting the co-existence of formal and informal international cooperation makes it impossible to examine the interactions and trade-offs that occur between different modes.

This special issue begins to fill these research gaps. Specifically, we focus on three sets of research questions:

  • First, what forms of informality can we identify inside and outside FIGOs? What do these different forms look like? Who participates in them? What are the commonalities and differences among them?

  • Second, is the shift toward informal modes of global governance actually happening on a large scale? If so, what forms does the shift take, and what temporal trajectories can we observe? Are there some issue areas changing more, or more rapidly, than others?

  • Third, what are the major drivers of the shift to informal governance? Are there functional demands for the governance of particular problems that international treaties and FIGOs address insufficiently or not at all? Do states desire flexibility in times of uncertainty? Or are the distribution of power and the interests of powerful players the major driving forces? What role do domestic political processes play? Are different types of informality shaped by different driving factors? How do causal factors interact in shaping the choice of informal institutional forms?

This introduction provides theoretical and empirical background and guidance for the exploration of these questions. The following three sections are structured around the three sets of questions just identified. First, we develop a typology of informality that highlights informality of, within, and around global governance institutions. Second, we provide an empirical overview of the recent growth of informal institutions in the international system, focusing on TGIs and IIGOs, as compared to the trajectory of FIGOs. Third, we outline a set of factors that are potential drivers of the growing importance of informal modes of global governance. We treat these as candidate explanatory variables and draw them from the literatures on international cooperation and global governance. In the fourth section, we introduce the other contributions to the special issue and discuss their major individual and collective findings. The final section outlines an agenda for future research on informal governance in world politics.

2 Three types of informal governance

Informality in contemporary global governance appears in a variety of forms. Based on the recent literature and the articles included in this special issue, we can identify three broad forms of informal governance: Informality of institutions, within institutions, and around institutions. Each type reveals a different aspect of the phenomenon of informality, and they are inter-related in important ways.

First is the emergence of informal governance institutions. The expansion of new institutional forms—IIGOs like the G8 and the G20 (Stone 2013; Cooper and Pouliot 2015), transgovernmental networks of domestic regulators, such as the Basel Committee on Banking Supervision (Raustiala 2002; Slaughter 2004), and TGIs like the Kimberley Process (Abbott and Snidal 2009; Westerwinter 2021)—means that it is no longer possible to discuss global governance in terms of treaties and FIGOs alone. Informal institutions that bring together diverse public and private actors have grown rapidly since the 1990s and are today an established element of the global governance architecture (Lake 2010; Abbott et al. 2016; Avant and Westerwinter 2016).

Several contributions to this special issue analyze the emergence and salience of informal institutions. Westerwinter (2021) documents the rapid growth of TGIs and how they vary in terms of issue areas, governance tasks, institutional design, and participation of public and private actors. Examining the factors that facilitate state participation in TGIs, he finds that countries with democratic political regimes are more likely to become involved and that the positive effect of democracy varies across issue areas in predictable ways. Carlson and Koremenos (2021) show that absolute monarchies, a specific type of autocratic regime, cooperate with one another using informal arrangements rather than formal treaties. They argue that absolute monarchs strategically choose informal modes of cooperation because the secrecy those modes make possible maximizes the mutual private benefits state leaders can reap from cooperation. The data presented in these and other articles in this special issue provide concrete measures of the scope and significance of informal institutions in world politics, something that case study and issue-specific approaches have struggled to achieve (Barnett et al. 2016).

Second, and somewhat more established in the literature, is the use of informal modes of governing within both formal and informal institutions. Most research on this type of informality has focused on informal arrangements, understandings, practices, or norms operating within FIGOs (Steinberg 2002; McKeown 2009; Stone 2011, 2013; Kleine 2013; Vreeland and Dreher 2014; Hardt 2014, 2018). These include internal routines, procedures, and structures that range from informal communication networks to methods of reaching consensus to habitual ways of selecting leadership. Yet informal practices are likely to be even more common in informal institutions, which lack constitutionally prescribed bodies and procedures.Footnote 2

In this special issue, internal informality is featured most prominently in Kersting and Kilby’s (2021) contribution, which analyzes US influence within the World Bank. They argue that the exertion of informal influence by the US over multilateral World Bank assistance is driven by the extent to which particular presidential administrations face Congresses with diverging preferences. In such situations, executive leaders prefer using informal influence in the World Bank over bilateral aid to pursue their foreign policy goals because it is more effective and less costly in domestic political terms. Their empirical analysis provides compelling evidence in support of this hypothesis.

Third, diverse informal institutions and networks exist around institutions of global governance. Often associated with transgovernmental initiatives or discussions of the “third UN” (Weiss et al. 2009), the literature on institutional communities includes work on transgovernmental networks (Keohane and Nye 1974; Raustiala 2002; Slaughter 2004; Bach and Newman 2010), transnational advocacy networks (Keck and Sikkink 1998), epistemic communities (Haas 1989, 1992), pluralistic security communities (Deutsch et al. 1957; Adler and Barnett 1998), transnational public-private partnerships (Börzel and Risse 2005; Andonova 2017), and issue campaigns (Carpenter 2010). Much, but not all, of the literature concentrates on emergent issue domains, framing issues, placing issues on global policy agendas, and implementation. Recent sociological research on ideationally homogenous transnational policy communities (Djelic and Quack 2010) integrates these institutional aspects into broader communities and networks.

In this special issue, this aspect of informality features in Reinsberg and Westerwinter’s (2021) investigation of informality in development assistance. It is also the focus of recent work on the role of transnational policy networks in facilitating policy reforms at the UN Security Council (Biersteker 2019), the impact of informal groupings on multilateral negotiations (Pouliot 2015; Onderco forthcoming), and the role of informal contact groups in post-conflict peacebuilding and crisis management (Prantl 2005, 2006; Whitfield 2010; Sauer 2019). For example, in his work on the role of permanent representatives in multilateral diplomacy, Pouliot (2015) demonstrates how informal networks among permanent representatives that operate in parallel to the formal structures and procedures of FIGOs shape how negotiations are conducted and which decisions are made. Similarly, Onderco (forthcoming) highlights the importance of informal networks of states for multilateral negotiations within the non-proliferation regime.

Distinguishing among informality of, within, and around institutions provides a first step in analyzing modes of informal governance in world politics beyond extant work on informal governance within formal organizations. The distinction is useful for descriptive purposes because it allows us to generate more fine-grained mappings of informal governance than would be possible by concentrating on any one type in isolation (Gerring 2012). It is also a powerful tool for generating and testing more fine-grained theoretical arguments. Specifically, focusing on the specificities of the three types of informal governance allows researchers to identify their particularities more sharply and to build more nuanced theories about the factors that lead to their emergence and proliferation. This is particularly important for specifying the causal mechanisms that link explanatory factors to the rise of informality. For example, power concentration might be conducive to some types of informality, but not to others. Similarly, a focus on the particularities of the different types allows researchers to uncover which specific aspects of domestic political institutions matter for different forms of informal governance.

3 From formal to informal global governance?

The institutional architecture of global governance has undergone dramatic changes in recent decades. The number of informal institutions, specifically IIGOs and TGIs, has been growing rapidly since the 1990s, both in absolute terms and even more so relative to FIGOs. We base our exploration of the growing importance of IIGOs and TGIs in world politics on a new dataset that allows for the comparative analysis of FIGOs, IIGOs, and TGIs over time and across issue areas (Westerwinter 2021, 2020).Footnote 3

3.1 Numbers

Starting with IIGOs, we observe that while in 1990 there existed only 28 IIGOs, their number increased to 82 by 2014.Footnote 4 This corresponds to a growth of about 193%. TGIs experienced even more rapid growth. From 74 in 1990, by 2014, their number increased by about 655% to a total of 559. These growth rates are consistent with the proliferation of informal global governance institutions that do not involve states as participants. Abbott et al. (2018: 10), for example, report that 116 transgovernmental networks have been created since 1990, while only 15 existed before 1990. Likewise, Abbott et al. (2016: 248) find that “private transnational regulatory organizations” formed by different combinations of civil society and business actors have proliferated in the past decades.

Although the absolute number of FIGOs (313) was still higher than that of TGIs (74) in 1990, by 2005, TGIs had become the most frequent form of cooperation in the data. In addition, between 1990 and 2014, the growth of FIGOs slowed dramatically to a rate of about 7% (see Fig. 2). Importantly, the flattening out in the growth of FIGOs co-occurred with the beginning of the sharp increase in the number of IIGOs, and even more of TGIs, in the late 1990s.

Fig. 2
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FIGO, IIGO, and TGI growth

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3.2 Issue areas

While the recent growth of IIGOs and TGIs is striking, it is not universal. Some issue areas witnessed more of a turn towards informal governance than others. Among TGIs, about 55% of all initiatives are concerned with environmental issues, including climate change and energy; 46% deal with development.Footnote 5 Forty-seven percent address social problems and 26% deal with health. Smaller numbers of TGIs also operate in other issue areas, including trade and commerce, human rights, technical issues, finance, and security.

The picture looks different for IIGOs. Here, 60% of the organizations in the database address security issues, 54% social problems, 52% environment issues, and 37% trade and commerce; 37% deal with development problems, 29% with technical issues, 20% with financial problems, and about 20% with health. FIGOs, by contrast, are most prominent in the areas of social affairs, development, trade and commerce, and technical issues (see Fig. 3).

Fig. 3
figure 3

FIGO, IIGO, and TGI issue areas

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Thus, the issue concerns of IIGOs and TGIs are not equally distributed, and they are not limited to the areas of environment, health, and human rights. They are also increasingly important for states that seek to address economic and security problems. In other words, informal institutional arrangements are an important instrument of governing in many issue areas of world politics.

3.3 Growth trajectories

The growth trajectory of informal modes of global governance, as well as their absolute numbers, has varied across issue areas. The creation of TGIs addressing the environment, development, and social affairs can be traced back to the 1970s. The growth rate increased slowly in the 1970s and 1980s, and then exponentially in the 1990s. We observe a similar growth pattern for TGIs operating in the health, technical, trade and commerce, and human rights areas, although here growth started later, and its rate has remained below that in environment, development, and social affairs. In finance, security, and human rights, the rate of TGI growth has remained low until today (see Fig. A-1 in the online appendixFootnote 6).

A different pattern emerges for the growth trajectories of IIGOs. Here, organizations that govern development, finance, and security issues emerged as early as the 1960s, and their numbers have increased considerably since then. IIGOs focused on environmental, social, trade, and technical problems have also increased rapidly in recent years, but this development only took off in the 1980s. IIGOs in the health and human rights areas appeared later, and their growth rates have overall remained lower than in the other issue areas (see Fig. A-2 in the online appendix).

The growth of FIGOs was most pronounced in the fields of development, environment, social affairs, technical, and trade and commerce, but has flattened out or even decreased slightly since the 1990s. FIGO growth has remained slower and lower in the finance, health, human rights, and security areas (see Fig. A-3 in the online appendix).

3.4 State participation

Another source of variation in informal global governance institutions is the pattern of state participation. Starting with TGIs, a small number of states, including the United States, the United Kingdom, Germany, and the Netherlands, participate in a large number of TGIs. Other states, including Russia, China, Brazil, and India, as well as many African and Latin American countries, are much less involved. However, along with the United States, United Kingdom, and Germany, Kenya and South Africa were among the top twenty TGI participant states in 2014 (see Fig. A-4 in the online appendix).

A different picture emerges for state participation in IIGOs. Here, countries such as China, Russia, India, and Brazil are among the most frequent participants (see Fig. A-5 in the online appendix). The twenty nations that are most frequently involved in IIGOs include China, Indonesia, South Africa, and Poland. Compared to both TGIs and IIGOs, the pattern of state participation in FIGOs is more balanced and universal, with a larger number of states being members of a larger number of organizations (see Fig. A-6 in the online appendix).

4 Explaining the informalization of global governance

Informal governance can be a strategy. States (and transnational actors) may select informal forms of governance because they perceive them as the best way to structure particular interactions and to govern particular problems, allowing them to achieve their objectives (whether substantive, political, or organizational) to the greatest extent possible. As with any strategic choice, the selection of informal modes of governance takes place in situations characterized by particular constraints and opportunities, which shape the costs and benefits that can be derived from available institutional designs.

Potentially then, the decision to govern border-crossing problems using informal rather than formal modes of cooperation can be shaped by a large number of variables. In this section, we draw on the broad literatures on international cooperation and global governance to identify candidate explanatory variables and consider how these may affect the emergence of informal global governance. Specifically, we draw on four major streams of theorizing on institutional choice in world politics—functionalist, power-oriented, domestic politics, and non-state actor-based theories—and derive from them specific variables that may help us to better understand variation in informal global governance institutions.

The contributions to this special issue use these independent variables, and others drawn from the same and other families of theories, to explain why states choose to govern informally. In their analysis of the rise of multi-stakeholder governance in the development domain, Reinsberg and Westerwinter (2021) explore the explanatory power of functionalist, power-oriented, domestic politics, and institutional context arguments. They find that the different theoretical strands, rather than being competing explanations, complement each other in explaining the proliferation of informal institutional arrangements. Westerwinter (2021) examines the factors that shape state participation in TGIs. His results suggest that domestic regime type, economic power, and internationally active NGOs affect countries’ decisions to participate in transnational governance initiatives.

Carlson and Koremenos (2021) focus on the relationship between domestic politics and informal cooperation among governments. They show that absolute monarchies are more likely to cooperate through informal agreements than democracies or pairs of states with different regime types. Kersting and Kilby (2021) also give pride of place to domestic politics, examining how it interacts with power in shaping informality within FIGOs. Focusing on US influence in the World Bank, Kersting and Kilby examine how domestic veto players with foreign policy preferences different from those of the executive create incentives for the executive to cooperate internationally through informal channels, allowing it to achieve its goals more effectively and at a lower cost.

The importance of particular factors is likely to vary across issue areas and types of informality. In addition, it is likely that in concrete empirical cases, a combination of causal factors, rather than individual variables in isolation, drives the selection and specific design of informal governance arrangements.

4.1 Functional considerations

The first wave of research on informal modes of global governance adopted a functionalist perspective, emphasizing the relative efficiency advantages of informality in solving collective action problems (Aust 1986; Lipson 1991; Abbott and Snidal 2000; Raustiala 2002; Prantl 2005; Benvenisti 2006; Kleine 2013; Koremenos 2016; Sauer 2019). Advocates of this perspective cite the greater speed and flexibility and the lower contracting costs of informal governance as major drivers of its proliferation (Aust 1986; Lipson 1991; Abbott and Snidal 2000; Raustiala 2002; Kleine 2013; Sauer 2019; Abbott and Faude forthcoming).

These benefits have become increasingly important as the transaction costs of international cooperation have increased. Throughout the twentieth century, the number of states has increased steadily. According to data provided by the Correlates of War (COW) Project, while only 45 states existed in 1910, this number increased to 75 in 1950, then further to 165 in 1990, and finally to 195 in 2014.Footnote 7 As the number of states rises, the costs of reaching international agreements increase (Oye 1985; Axelrod and Keohane 1985; Kahler 1992). More and more states with stakes in global problems demand access and seek to shape outcomes.

At the same time, the heterogeneity of state preferences has increased, especially in the wake of the waves of decolonization and the break-up of the Soviet Union. Preference heterogeneity further complicates reaching international agreements (Oye 1985; Kahler 1992). The same is true for governance through FIGOs. As the number of member states increases, governance slows down and often comes close to a standstill. Trade negotiations in the framework of the General Agreement on Tariffs and Trade and later the WTO are a case in point (Hale et al. 2013).

States can reduce these transaction costs by shifting action from cumbersome, formal intergovernmental treaties and organizations to smaller, more informal arenas. The diverse preferences and ideas that must be considered in seeking solutions to problems can be managed and altered more easily, in turn reducing the costs and time required to reach agreements. Thus, if the creation of informal governance arrangements is a functional response to the increasing costs of governing, then we should expect informal structures to be relatively small clubs of like-minded states rather than large, universal membership organizations.

The speed and flexibility with which informal organizations can be negotiated and adapted are particularly appealing for states confronted with problems characterized by uncertainty about the state of the world: A condition in which the future benefits and costs of particular forms of cooperation are not easily predicted. Such uncertainty makes governance structures difficult to design because the problems and available solutions are poorly understood and subject to frequent change (Koremenos et al. 2001; Thompson 2010; Kleine 2013). Uncertainty can be scientific or technical, but it can also relate to political or economic issues. For example, the states that collaborate in the Inter-American Tropical Tuna Commission initially knew little about how fishing techniques affect dolphin mortality and had no precise idea how to accomplish their shared goal of preserving Eastern Tropical Pacific tuna stocks and protecting dolphins. This uncertainty made devising specific policies and organizational structures difficult and prompted institutional experimentation (de Búrca et al. 2013).

Incorporating flexibility measures, such as termination or sunset clauses, in formal intergovernmental agreements and organizations can facilitate cooperation under uncertainty (Kucik and Reinhardt 2008; Helfer 2013; Koremenos 2016). Importantly, however, while flexibility provisions in FIGOs are typically designed to allow responses to unforeseen exceptional circumstances, the speed and flexibility of IIGOs and TGIs result from the fact that their rules and procedures deliberately remain informal (Aust 1986; Lipson 1991; Abbott and Snidal 2000). This is a more fundamental feature than flexibility clauses. It enables actors to continuously learn and redefine the problems they face, and to readjust the processes needed for solving them quickly (de Búrca et al. 2013). This makes it easier to reform governance procedures, and even to change the actors involved, as new information about the problem and potential solutions becomes available (Reinsberg et al. 2017). Informal institutions are thus well-suited to deal with problems and issue areas characterized by persistent uncertainty about the state of the world.

In sum, from a functionalist perspective, the number of states and transnational actors involved in governing, the heterogeneity of their preferences, and the increasing technical and political complexity of problems (which increase governors’ uncertainty about the state of the world) are candidate explanatory factors for the growing importance of informality in world politics. In this view, if informality is used by states to reduce the number of actors involved in governing, we would expect increases in the number of states involved in a cooperative effort to be negatively associated with the likelihood of informal global governance. If, by contrast, informality is a response to the high transaction costs of cooperation with large numbers, then we would expect an increase in the number of states to have a positive effect on the likelihood of informal governance. We also expect preference heterogeneity and uncertainty about the state of the world to have a positive effect.

In this special issue, Reinsberg and Westerwinter (2021) explore the effect of both number of states and preference heterogeneity on the likelihood of TGIs being chosen as instruments of cooperation in the development area. Their results indicate a negative effect of the size of cooperating groups and a positive effect of preference heterogeneity on the choice of informality.

4.2 Power

Power-oriented theories of international institutions suggest that the creation and design of global governance arrangements are a direct result of the preferences of powerful players (Krasner 1991; Garrett 1992; Gruber 2000). Consequently, as the distribution of power among states and transnational actors changes and/or the preferences of powerful players change, shifts in the institutional architecture are likely to occur.

The same factors are said to be at play with informal governance arrangements. States use informal institutions to project power and realize more favorable outcomes (Stone 2011, 2013; Westerwinter 2013; Avant and Westerwinter 2016). The resulting institutions are not always, perhaps not even most of the time, efficient responses to collective action problems (Moe 1990; Krasner 1991). We therefore expect that a state’s decision to choose informal modes of cooperation reflects political processes that underlie bargaining over institutional design.

Research on informal governance within FIGOs suggests that informal rules and procedures are a strategy of powerful states with substantial institutional capacity, such as the US or the EU, to secure their control over organizational operations in times when their preferences are strongly implicated (Stone 2011). In exchange, major powers transfer to weaker states disproportionate formal control over operations during ordinary times. In other words, formal procedures within FIGOs for information-sharing, agenda-setting, proposal-making, and voting weaken the relationship between structural power and control over outcomes, distributing power more widely among participants (Stone 2011). Powerful players then use informal governance to bypass these formal constraints (Steinberg 2002; Stone 2011; Kilby 2013).

In similar fashion, informal governance outside FIGOs may be a strategy of powerful players to achieve outcomes in line with their preferences. Compared to FIGOs, informal international institutions impose fewer constraints on power and thereby increase the returns to power. This creates incentives for powerful players to favor informal arrangements (Vabulas and Snidal 2013).

Informal institutions rarely grant formal access or voting rights to weaker actors. In fact, they rarely grant them to any actor. Thus, they leave powerful actors freer to dictate policy by exploiting their superior agenda-setting power and bargaining leverage (Steinberg 2002). Recognizing these advantages, powerful states have strong incentives to participate in informal institutions, particularly in situations where their preferences are strongly affected.

According to this logic, we should expect that powerful states and transnational actors will be more likely to participate in informal institutions because they can expect to benefit most from the influence and room for maneuvering that informal rules and procedures provide. However, informal governance structures may also be a source of power in their own right and may even empower otherwise weak players, such as small states and NGOs (Vabulas and Snidal 2017; Avant and Westerwinter 2016). As a consequence, such actors may be particularly inclined to join informal institutions as a way to improve their bargaining position.

In sum, from the perspective of power politics, the power of the actors involved in addressing a particular problem is a potential explanatory variable for the selection of informal institutions. Existing research provides examples of both strong and weak actors opting for informal strategies, and several of the papers in this special issue explore the existence and directionality of this possible causal relationship. Westerwinter (2021), for example, finds that economically powerful countries are more likely to become involved in TGIs. Similarly, Reinsberg and Westerwinter (2021) show that cooperation in the development area is more likely to take the form of TGIs as the economic power of the countries involved in the cooperative effort increases. Kersting and Kilby (2021) find that governments of powerful countries exert informal influence in FIGOs, and their incentives to do so are shaped by the domestic political context in which they operate.

4.3 Domestic politics

Domestic politics is another candidate driver of informality of, within, and around global governance institutions. Of particular relevance in this context is a state’s political regime type. The governments of democratic states must adhere to a range of legal-procedural requirements for policy-making (Tsebelis 1995). These apply not only to domestic policy-making but also to international policy-making (Mansfield and Milner 2012). Executives must consult legislatures when forming foreign policy preferences; must seek legislative approval of treaties; and must negotiate the domestic implementation of international commitments with the political opposition and interest groups from all sectors of society (Simmons 2000; Dai 2005; Mansfield and Milner 2012).

At a time when many international policy problems are of a daunting complexity, technically and politically, these domestic requirements can be the source of considerable costs for state executives (Snidal and Thompson 2003). Throughout the policy process, the executive must achieve agreement with both international and domestic veto players, making it more difficult to realize policies close to its own preferences (Milner 1997; Milner and Peter Rosendorff 1997; Martin 2000). This is of particular relevance when veto players have preferences on particular issues that differ from the executive’s own (Milner 1997; Lupu 2015).

One way for democratic leaders to reduce these costs, and to realize policies closer to their own preferences, is to opt for modes of international cooperation that are less demanding in terms of domestic politics than FIGOs and treaties. Informal international institutions require less, or even no, involvement of domestic veto players in the making and implementation of foreign policy. The rules created by informal institutions do not take the form of treaties and therefore do not require approval by domestic legislatures (Aust 1986; Lipson 1991; Abbott and Snidal 2000). Informality is also associated with reduced visibility, reducing the likelihood that domestic opponents will take note of and respond to the executive’s actions (Greven 2005; Stone 2011). In addition, informal institutions are often characterized by selective participation, excluding troublesome actors (Westerwinter 2013). In sum, informality creates informational and access advantages for executives vis-à-vis domestic opponents and makes it more difficult for opponents to follow and influence the executive’s actions.

While these factors create incentives for democratic governments to participate in informal institutions, those incentives are likely to be weaker for autocratic governments. In autocracies, the formal legal requirements that governments must observe in designing and implementing foreign policy are, all else equal, less elaborate and demanding than in democracies. National parliaments often have little power vis-à-vis executives; legislative approval of international agreements is often not required; and domestic veto players are either absent or have preferences in line with those of governments. As a consequence, all else being equal, the benefits to autocracies from participating in informal international institutions are less pronounced than those reaped by democracies: Autocrats already enjoy many of the domestic politics benefits of informal cooperation. However, as Carlson and Koremenos (2021) discuss, autocratic regimes may have other reasons to use informal modes of cooperation, especially when interacting with other autocracies.

A focus on domestic politics thus suggests two additional candidate explanatory variables, domestic democracy and domestic veto players. We expect both to support the choice of informal modes of governance. As countries become more democratic and/or have a larger number of domestic veto players capable of obstructing government policy, informality becomes increasingly attractive to executives. All the contributions to this special issue discuss the role of domestic politics in states’ choice of informal global governance. Reinsberg and Westerwinter (2021) as well as Westerwinter (2021) find that domestic democracy promotes the choice of TGIs, whereas Kersting and Kilby (2021) find that the existence of domestic veto players with opposing foreign policy preferences incentivizes the executive to pursue its foreign policy goals using informal governance instruments. By contrast, Carlson and Koremenos (2021) show that absolute monarchs are more likely to cooperate with each other through informal, secretive agreements, suggesting that domestic regime type may affect different types of informality differently and that the relationship between domestic politics and informal global governance requires more nuanced theorizing.

4.4 Non-state actors

Non-state actors have become increasingly important for global governance (Hall and Biersteker 2002; Avant et al. 2010; Green 2014). It is difficult to measure accurately the number of non-state actors active globally. One proxy is the number of international NGOs (INGOs). Data from the Yearbook of International OrganizationsFootnote 8 reveals exponential growth in the number of INGOs across countries, beginning in the early twentieth century.

Global problems are complex, both technically and politically, and no individual actor controls the knowledge and resources required to effectively and efficiently deal with them (Avant et al. 2010). In addition to states and intergovernmental organizations, business actors and NGOs often possess essential expertise (Abbott and Snidal 2009). NGOs may also contribute to the mitigation of democratic legitimacy problems by voicing the interests of stakeholder groups that otherwise lack access to governance processes.

One way to incorporate the resources of businesses and NGOs in governance is to open up FIGOs for their participation (Tallberg et al. 2013). Another way is to create institutions that allow for collaboration between states and non-state actors on a more equal footing, notably TGIs (Westerwinter 2021). Some TGIs bring together governments, business, and NGOs to create and implement rules and standards to govern the negative consequences of corporate and state conduct, as well as other problems. In contrast to traditional state-based governance forms, in TGIs, non-state actors are not only the objects of governing, but stand at the center of the governance process itself, including decision-making, implementation, monitoring, and enforcement (Abbott and Snidal 2009; Avant et al. 2010).

In sum, the growing importance of informal modes of global governance may be driven in part by attempts to create institutional structures that allow the increasingly large number of globally active non-state actors to participate in decision-making and implementation. Such participation integrates the expertise and other resources of non-state actors, and can contribute to the effective, efficient, and legitimate provision of global public goods. We expect that, as the number of non-state actors operating in a specific governance area grows, the tendency to choose informal means of cooperation that allow for their inclusion will become stronger.

In his contribution to this special issue, Westerwinter (2021) argues that one reason why democracies are more prone to become involved in TGIs is that domestic non-state actors, such as business and NGOs, can create domestic demand for transnational governance, to which governments can respond by joining TGIs (see also Abbott and Faude forthcoming). His empirical finding of a positive effect on state participation in TGIs from both domestic democracy and the number of internationally-operating NGOs in a country supports this argument.

5 Contributions to the special issue: Findings and conjectures

Many analyses of global governance either ignore informality altogether or focus only on informal governance within FIGOs, creating a gap between the theories and practices of world politics. Building on the pioneering works cited above, the contributions to this special issue take informality in world politics seriously. They develop new theoretical arguments about the emergence of different types of informal governance. Using new, innovative data, they demonstrate that diverse modes of informal governance inside and outside of FIGOs have grown in numbers and importance in nearly all issue areas of world politics. In doing so, the contributions apply our typology of informality of, within, and around international institutions to chart new theoretical and empirical ground. Carlson and Koremenos, Reinsberg and Westerwinter, and Westerwinter examine different types of informal forms of cooperation among states as well as states and non-state actors. Kersting and Kilby investigate informality within FIGOs.

As noted above, the articles also begin to uncover the driving forces underlying the growth in different types of informal global governance, drawing on functionalist, power-oriented, domestic politics, and non-state actor explanations. Kersting and Kilby identify power and domestic politics as major explanations for informal influence within the World Bank; Carlson and Koremenos link domestic politics and informal agreements among governments; Reinsberg and Westerwinter test functionalist, power-oriented, and domestic politics arguments about the selection of informal governance in the development area; and Westerwinter explains state participation in TGIs based on variation in domestic politics, power, and the presence of internationally active NGOs. Together, the contributions to this special issue unveil and explain central parts of the institutional architecture of global governance that traditional analyses have overlooked.

Turning to the individual articles, Kersting and Kilby (2021) explore how power considerations in interaction within domestic politics can spur informality within FIGOs. They examine whether US presidential administrations exert greater informal influence within international financial institutions when they face an uncooperative Congress, and thus have less domestic control over bilateral aid. Reexamining four empirical studies of US informal influence within the World Bank, they demonstrate that informal influence is greater in years with a divided US government. Thus, their analysis indicates that power helps to explain the use of informal governance within the World Bank. However, it is not power per se, but its interaction with the domestic political configuration, which drives the US’s use of informality in the World Bank. Compared to previous studies, this provides a richer picture of when and why the US exerts influence in multilateral settings, and an alternate explanation to persistent questions about the role of international organizations in the international political economy. Their analysis is also an insightful example of how different explanatory factors can interact in shaping the selection of informal governance instruments.

Carlson and Koremenos (2021) focus on informal cooperation among governments as an alternative to FIGOs and formal treaties. They develop a theoretical argument centered on domestic regime type to explain variation in states’ use of this type of informality of international institutions. Carlson and Koremenos set out to explain the low levels of formal cooperation between authoritarian monarchies. They argue that, rather than failing to cooperate, authoritarian monarchies frequently do cooperate with one another, but do so informally. The limited rule of law in absolute monarchies, especially the prevalence of unilateral and non-transparent policy making and implementation, engenders an absolutist logic, leading executives to prefer similarly personalist and secret informal agreements when interacting with other absolute monarchs. Based on statistical analysis and a case study of informal, secret cooperation among the members of the Gulf Cooperation Council, they find that jointly absolute monarchic dyads have higher levels of informal cooperation than jointly democratic dyads and dyads of mixed regime types. By contrast, where authoritarian monarchies enter into agreements with other regime types, they rationally and strategically accept the formal design mechanisms necessary for efficient cooperation. Carlson and Koremenos shed important new light on the relationship between domestic regime type and informal global governance and show that also autocratic regimes can have incentives to use specific types of informality when entering into international cooperative arrangements.

Oliver Westerwinter (2021) expands the analysis to instances of informal cooperation among public and private actors. Using a unique dataset of 636 TGIs established between 1885 and 2017, he demonstrates the rise and proliferation of these public-private governance arrangements across time and issue areas and uncovers patterns of variation in terms of the governance tasks, participants, and institutional designs of TGIs. He also explores how domestic politics, power, non-state actors, and other factors influence states’ involvement in TGIs, and he finds that democratic countries are especially prone to join TGIs, but that this effect varies across issue areas. He explains this with the increased demand for and supply of transnational governance participation in democracies that results from the involvement of NGOs and business actors in domestic governance. This lends support to the argument that democracies have incentives to cooperate through informal institutional forms but offers the role of domestic non-state actors as an additional causal mechanism.

In their contribution, Bernhard Reinsberg and Oliver Westerwinter (2021) examine when states choose informal governance arrangements in the development domain. They show that since the end of the Cold War, international development cooperation has increasingly become informal. They consider functionalist, power-oriented, domestic politics, and institutional context-oriented explanations for the use of informal governance institutions in the form of TGIs. Their analysis is based on a mixed-methods research design that combines quantitative and qualitative methods. Importantly, their quantitative analysis employs a selection model that takes into account the drivers of the creation of new international institutions when examining the factors that facilitate the choice of a TGI design. In both their quantitative and qualitative analysis, the authors find consistent support for functionalist, power-oriented, domestic politics, and context-oriented arguments. Their analysis shows that different theoretical perspectives are complementary rather than competitive when it comes to explaining states’ choice of informal global governance arrangements.

Finally, in her concluding remarks, Lisa Martin (2021) discusses some of the questions that the contributions to this special issue leave unanswered and identifies elements of an agenda for future research on informal governance in world politics that are complementary to those we present below.

In sum, there is consensus among the authors on the substantive importance of informal governance in world politics. This is striking given the broad range of issue areas and institutional forms the contributions consider. Taken together, moreover, the contributions broadly support our argument that the phenomenon of informal governance in world politics is broader than informal practices and norms within formal organizations: They aptly demonstrate the rise and proliferation of informality of and around global governance institutions, as well as within them.

There is less agreement, however, on the underlying causes of these developments. All four sets of candidate explanations identified in this introduction—functional considerations, power, domestic politics, and non-state actors—find support in the contributions. Importantly, however, most authors find evidence in support of more than one explanation. This suggests that explanations based on different theories of global governance are complementary, rather than competing, in explaining states’ choices of different types of informality.

In addition, the contributions identify additional insights, puzzles, and conjectures regarding the rise of informal global governance and how to study it; these provide a strong basis for future research. We summarize the most interesting of these here.

First, the contributions offer insight into the rise of informality in world politics. In addition to the informal exercise of state power within FIGOs, the contributions provide compelling evidence that additional types of informal governance have proliferated and become important in a broad range of issue areas. Compared to extant case studies and issue area-focused analyses, the evidence they provide allows for systematic, cross-issue area assessment of an important type of global governance. Given the lack of prior large-n data on informal global governance, these are important descriptive inferences that will help to advance research (Gerring 2012). Important puzzles that emerge from these descriptive assessments include why we observe an increase in the informality of international institutions only in the 1990s and not before, and why the proliferation of informal governance is more pronounced in some issue areas than in others.

Second, while power is an important driver of informal governance, the picture is more complex than previous work suggests. International power disparities can interact with domestic factors in shaping informal governance, and power also matters for the choice among forms of informality. There is also evidence in the wider literature in support of the hypothesis that informal governance arrangements can be strategies of weaker players, including both weak states and NGOs (Vabulas and Snidal 2013; Avant and Westerwinter 2016). Informal institutions provide NGOs with the possibility of increased influence in the governance of problems they care about. As a result, they may lobby their governments to act through informal institutional arrangements. An important task for future research, then, is to examine in greater detail the conditions under which informal global governance is used as a strategic tool by powerful players or weaker ones. Research will also benefit from more nuanced theorizing of the interaction of power and other variables.

Third, domestic politics clearly matter for the selection of informal modes of governance, but informality has different implications for different actors. Informal governance has relatively limited transparency to actors that are not involved (Aust 1986; Lauth 2000; Greven 2005; Stone 2011). It thus has the potential to limit participation and make it more difficult to hold decision-makers accountable (Herz and Hoffmann 2019). However, informality may also enhance access and participation by actors, such as NGOs and business groups, who often face difficulties in becoming involved in FIGOs (Andonova et al. 2017).

Informality also has significant implications for countries with different domestic political regimes. While autocratic leaders may prefer informal cooperation for its secrecy and lack of transparency and participation, governments of democracies may also find the secrecy and non-transparency of informal governance attractive, particularly when they face strong domestic veto players with policy preferences that diverge from their own. Democratic regimes may also choose informal institutions because they allow for increased participation by non-state actors who seek to become directly involved in global governance.

In short, the same features of informality may attract particular regime types for different reasons; while one type may use one mode of informality for one reason, it may use a different mode for a different reason. This suggests that a fruitful area for future research lies in more nuanced theorizing about the relationship between domestic politics, particularly domestic regime type, and different forms of informality in world politics.

Fourth, the articles make important methodological contributions. Most existing studies of informality in world politics are based on one or a small number of cases (Prantl 2006; Stone 2011; Kleine 2013; Hardt 2014, 2018) or focus on particular issue areas, such as climate change (Bulkeley et al. 2014), sustainable development (Andonova and Levy 2003), or energy (Szulecki et al. 2011). As a consequence, findings are likely to suffer from problems of selection bias, and it is questionable to what extent results can be generalized. In addition, existing research often neglects selection problems, i.e., the fact that we only observe the design of institutions actually created. By contrast, the contributions to this special issue introduce and analyze new, large-n datasets with information on different forms of informality, in multiple issue areas, and for extended time periods. Importantly, some contributions take selection effects into account when analyzing the drivers of informality. Their results shed important new light on existing case study findings and open new avenues of research on informal governance. In addition, the papers show that combining quantitative and qualitative methods and data can reveal important insights about informal governance.

Finally, the articles in this special issue address the well-known difficulty of measuring informal governance arrangements, which often leave limited public paper trails (Christiansen and Neuhold 2012; Koremenos 2013; Hardt 2014). The contributions suggest a variety of methods for measuring informality: An indirect strategy of exploring the enforcement of conditionality, speed of loan disbursement, project ratings, and timing of loan disbursements in the World Bank; using event data to generate a measure of informal cooperation; and a new dataset that captures whether FIGOs and TGIs have independent secretariats, specified decision-making procedures, monitoring, enforcement, and dispute settlement mechanisms.

Thus, based on innovative data and approaches, the contributions indicate ways in which researchers can distinguish empirically between informal and formal global governance, and can explore differences in the degree of informality across institutions. The latter, in particular, provides a starting point for developing more fine-grained, continuous measures of informality that allow researchers to move beyond categorical measures and operationalize the intuitive idea that informality is a continuous rather than a binary phenomenon (Vabulas and Snidal 2013).

6 Conclusions: A research agenda on informal global governance

The goal of this special issue is not to provide or test a single theory of informal global governance, but rather to provide a set of analyses that speak to a common set of theoretical, empirical, and methodological questions. More broadly, the goal is to advance the emerging research agenda on informality in world politics, and the articles in this special issue suggest multiple avenues for future research beyond those just indicated. We conclude by highlighting three.

First, while we set out to map and explain the proliferation of three distinct types of informality in world politics (of, within, and around international institutions), the contributions suggest that more nuanced theorizing of informality and its drivers is needed. Ideal types of informality provide a good basis for identifying different aspects of a broad phenomenon and for developing hypotheses about their emergence. However, as Lisa Martin (2021) rightly observes, this approach also impedes inquiry into variation within broad types.

For example, the contributions demonstrate rich variation among TGIs in terms of governance tasks, issue areas, participation, and institutional design. They also show that informal and formal design elements may be combined within the same institution. With respect to the drivers of informality, the contributions find that different aspects of domestic democracy, such as veto players, participatory governance norms, and non-state actor involvement, are linked to different aspects of informality. They also show that autocratic regimes may choose informality for the same reasons as some democracies do. These are important insights that contribute to a more nuanced understanding of informality in world politics. Similarly, more nuanced theorizing may prove fruitful with respect to power-oriented theories, functionalist claims, and other theoretical arguments.

The contributions similarly suggest a need for more fine-grained data. While they collectively present innovative and systematic quantitative and qualitative data, more is needed. In particular, in addition to detailed cross-section data on different types of informal institutions, researchers would benefit from collecting time-series cross-section data to explore the factors that account for the rise of informality over time. Likewise, more detailed and tailored qualitative data based on primary documents, interviews, and participant observations will be needed to subject nuanced theoretical arguments about the drivers of informality to systematic empirical tests.

Second, while this special issue demonstrates the proliferation of different types of informality in world politics, it is critical to examine systematically the implications of this proliferation for the effectiveness and legitimacy of global governance. Existing works suggest that informal governance has the potential to strengthen both effectiveness and legitimacy (Keck and Sikkink 1998; Reinicke and Deng 2000). However, the lack of access and participation for relevant actor groups, often characteristic of informal cooperation, also has the potential to undermine their effectiveness (by excluding important expertise and resources) and their democratic legitimacy (by excluding relevant voices) (Abbott and Snidal 2009; Westerwinter 2013, 2016).

Thus, the consequences of informal cooperation are an important topic for future research. Can informal modes of international and transnational cooperation deliver, effectively addressing global problems? Or are they empty shells with little, if any, impact? What is their impact on the inclusiveness of global governance? Do they empower weaker actors, such as NGOs, small states, and rising powers? Or do they merely manifest and reinforce existing distributions of power? Do they improve the transparency and accountability of contemporary global governance institutions, or do they further weaken them?

Finally, a logical next step from the analyses in this special issue is to consider interlinkages across different types of informal and formal institutions. Due to the rapid proliferation of diverse informal and formal modes of institutionalized cooperation, today’s global governance includes a broad range of institutional forms with different sets of state and non-state participants (Lake 2010; Avant et al. 2010; Avant and Westerwinter 2016). These forms overlap and intersect in multiple ways, forming institutional complexes of interdependent and interacting organizations (Raustiala and Victor 2004; Abbott 2012). Reinsberg and Westerwinter (2021) begin to explore how institutional design choices are shaped across organizational forms. Building on this and other work in this special issue should help scholars to explore the consequences of institutional context on institutional design choices.

Taken together, this research agenda promises to bring about a more sophisticated understanding of the emergence and effects of different types of informal global governance institutions. Such research will also inform theories of international cooperation more generally as these currently focus disproportionately on formal treaties and organizations. Finally, this research agenda can lead to a better understanding of the complex interdependencies among different types of formal and informal institutions as well as the creation, design, and consequences of contemporary global governance arrangements.