Social constructivism has come of age in contemporary international relations (IR) theory. Indeed, more and more submissions to presses and journals in both Europe and America characterize themselves as constructivist or situate their arguments vis-à-vis those of constructivists. In substantive terms and as the three books under review attest, constructivists also now offer detailed empirical studies that amplify and enrich their earlier conceptual and meta-theoretical critiques of mainstream approaches. Yet, as with any maturing research program, there are gaps to be filled and challenges to be met. These include a better appreciation and theorization of domestic politics; more explicit attention to research methods; further work on the linguistic turn so central to much of constructivism; and, finally, a rethink of attempts to build bridges and, in particular, of the difficulties and tradeoffs involved in such efforts.