Alexander Wendt's book, Social Theory of International Politics, is published twenty years after Kenneth Waltz's enormously influential Theory of International Politics. The similarity in their titles is no coincidence, since Wendt wants to build on the insights of Waltz's realism and construct an idealist and holist account of international politics (not, note, international relations). In my view, Wendt's book is likely to be as influential as Waltz's. It is a superbly written and sophisticated book, one that has clearly been drafted and redrafted so as to refine the argument and anticipate many of the likely objections. I think that although I can anticipate the objections of both his rationalist and his reflectivist critics. I am also aware that he makes life difficult for them by defining his ground very precisely, and by trying to define the terms of any debate in which he might be engaged. Criticism of the book is not an easy task. The book is likely to become the standard account for those working within the social constructivist literature of International Politics. It is a book that has been eagerly awaited, and it will not disappoint those who have been waiting for Wendt to publish his definitive statement on constructivism.