How do regime complexes as social orders affect relations among international organizations (IOs)? This article explores this question by studying the longitudinal development of interorganizational practices and the social meanings attached to these practices that constitute a regime complex. Adopting a practice lens, our analysis redirects scholarly attention from rationalist accounts of strategic interactions between IOs to the study of patterned "doings"among actors in regime complexes. The mixed-methods analysis of interorganizational practices between eight IOs in the global health regime complex shows that cooperation among IOs is not primarily the outcome of rational responses to problems of collective action. Rather, IOs engage in similar types of practices because they want to be considered "good"IOs that follow a repertoire of habitual and appropriate practices. In turn, interorganizational practices create social meanings that constrain IOs. The approach put forward in this paper demonstrates the ordering effect of practices on the global health regime complex.