Research on international cooperation has made substantial progress by taking seriously the formal details of international institutions, such as international organizations (IOs) and treaties (Goldstein et al. 2000; Koremenos et al. 2001; Hawkins et al. 2006; Thomson et al. 2006). Formal rules do not, however, exhaust the institutional variety of international cooperation. They are often inadequate descriptions of the game that actors play in world politics (Achen 2006; Stone 2011, 2013). As Stone (2011) argues, IOs are governed by both formal and informal rules, and powerful states exploit informal governance to manipulate IO policies when their interests are acutely affected. For example, the rules of the game played in the World Trade Organization depart substantially from the formal treaty provisions (Steinberg 2002). Likewise, in the European Union (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 (Kleine 2013). As these examples indicate, while formal rules are important features of contemporary global governance, in many situations informal practices may override, substitute for, or complement the formal provisions.
Most of the recent works on informal governance in international relations focus on informality within formal IOs (Stone 2011; Kleine 2013; Kilby 2013). However, as the volume Informal International Lawmaking edited by Joost Pauwelyn, Ramses Wessel, and Jan Wouters convincingly describes, the phenomenon is broader than this. The contributions to the volume cover a broad range of over 30 cases 1 of informal international cooperation ranging from informal procedures within IOs to informal groups of states and transnational networks of government bureaucrats. These contributions develop innovative theoretical arguments about the emergence, operation, and consequences of informal modes of international cooperation; discuss the location of such informal modes within the “universe of law”; investigate how informal modes of cooperation interact with formal international law; assess the legitimacy and democratic accountability of informal modes of cooperation; and analyze how informal modes of cooperation are elaborated and implemented by domestic institutions. The volume concludes with a chapter that summarizes the contributions of the other chapters, outlines areas for future research, and articulates practical guidelines for negotiators and actors who are involved in the elaboration of informal international law.