Transnational rule-making organizations have proliferated in the area of sustainability politics. In this article, we explore why these organizations share a set of core features that appear overly costly at first sight. We argue that norms that evolved out of the social interaction among transnational rule-making organizations account for this phenomenon. Thus, in the early 1990s, an organizational field of transnational rule-making has gradually developed in the field of environmental politics. Responding to a broader social discourse about global governance that stressed a need for innovative forms of cooperation among different societal sectors, this organizational field gained in legitimacy and strength. A set of commonly accepted core norms, the increasing density of interaction among the field's members, and the success and legitimacy ascribed to the field's key players by the outside world helped to solidify the organizational field until it eventually developed a 'life of its own'. © The Author(s) 2009.