Why do states choose informal organizations to govern global challenges? Using the global development regime as a piloting case, this article argues that different informal organizations serve different purposes. Informal intergovernmental organizations generate “club benefits” for member states, which arise from executive policy coordination behind closed doors. In contrast, transnational governance initiatives allow states to reap “risk-sharing benefits” in the production of global public goods by involving stakeholders. Using regression analysis for a set of development-related institutions, the analysis demonstrates that the two types of organizations are driven by different motivations. Complementary evidence is provided through case studies of two institutions: The IBSA Dialogue Forum (an informal intergovernmental organization) and the Global Partnership for Effective Development Cooperation (a transnational public-private partnership). The findings inform conceptual discussions of the informality of institutions while contributing to a better understanding of the design determinants of informal organizations.