Contrary to what is usually implied by work on the relationship between political opportunity structures and social movements, political institutions are not a general setting offering or denying formal access and political opportunities to every challenge, but rather favor certain types of movements and constrain others. This process of institutional selectivity depends on the relationship between the structure of a given political institution and the movement type and defines social movements as pro-institutional, counter- institutional, or neutral. Accordingly, variation in the movements' action repertoire and degree of success can be observed. Yet, political institutions leave the door open to different interpretations by social actors so that a framing struggle takes place; at stake is the fit between movement demands and the structure of political institutions. The argument is developed through the example of federalism and its impact on two types of movements-namely, regionalist and squatters' movements-and illustrated by discussing their fate in France, the Netherlands and Switzerland. Empirical data suggest that institutional selectivity is to be taken into account to reach a better understanding of the relationship between social movements and their political context.