This article provides a partial but necessary review of the dominating themes, evolution, and pending tasks that await the comparative politics of federalism. The basic premise of this article is taken from rational choice institution-alism. The article fist delimits federalism as an institution, before it pays attention to the impact of federalism on democracy and the workings of the economy. An analysis of federalism as an endogenous institution is provided. The article also mentions a number of methodological considerations on the comparative study of the origins and consequences of federalism. It ends with a discussion of the various challenges that lie ahead of the field.