This article outlines the virtues of a usually unturned stone in the field of institutional theories, i.e. a political institutionalism. By rejecting the emerging approaches centred on existing institutions as a reference model for a political version of institutionalism and by moving away from the more time-tested sociological and legal versions of it, the political institutionalism that this article sketches is based on three main tenets: 1) the interstitial character of institutional practices; 2) the normative relevance of customary norms (as both the final outcome of the institutional process and an orienting principle for interpreting the law); 3) the irreducibly political – that is, essentially non-juridical – essence of a given set of normative contexts (or eventually a given set of contextual principles and criteria deeply influencing any normative context). In addition, the article aims at carving out the proper place of political institutionalism in current political scholarship by emphasizing three analytical tools that can be of some help in dealing with the process of formation and decay of political institutions (be they broadly or narrowly conceived).