Regime theory seeks to explain policy convergence among states, but focuses almost exclusively on agreement at the level of the international system or in particular historical eras. This dissertation provides an alternative account of the micro-level social construction of multilateral institutions, which occurs as member states meet in continuous session to debate common policies. In these verbal exchanges, states incur informal commitments that accumulate over time. This cumulative body of group commitments helps foster consensus in a growing number of policy areas. Building on Durkheimian sociology, pragmatic linguistics, ethnomethodology, rhetoric and argumentation theory, I develop an analytical framework to study the functional aspects of groups and comity. An analysis of NATO and IMF cases of debate confirms that authoritative informal commitments, group affiliation and social pressure help drive policy consensus. It also finds a distinction between the type of group solidarity in NATO, and solidarity among IMF members later in that institution's history