Why do actors in international society succeed in forming institutional arrangements or regimes to cope with some transboundary problems but fail to do so in connection with other, seemingly similar, problems? In this article, I employ a threefold strategy to make progress toward answering this question. The first section prepares the ground by identifying and critiquing the principal models or streams of analysis embedded in the existing literature on regime formation; the second section articulates an alternative model, called institutional bargaining. The third section employs this alternative model to derive some hypotheses about the determinants of success in institutional bargaining and uses these hypotheses, in a preliminary way, to illuminate the process of regime formation in international society.