The constitutional role of political parties is one of the most typical features of the European constitutions of the second half of the twentieth century, requiring the elaboration of a constitutional notion of the political party. This article therefore aims to examine this conceptual elaboration in Italy, in the years between 1943 and 1948, beginning with the constitutional theories of the late 1930s and ending with the work of the Constituent Assembly. In that debate, which was not straightforward and whose outcome was far from obvious, both jurists and the parties themselves took part, displaying however different approaches and—more importantly—different constitutional cultures.