The volume offers a reconstruction of the concept of political party, created by the constitutional culture of the Italian Liberals in a span of time going from the second half of the 19th century to the start of the fascist regime. The goal is to investigate how the Italian rule of law accepted, reinterpreted and built its idea of a political party, what role it attributed the party on the social and institutional levels, and how it finally included it within its form of government. The volume is divided into two parts. The first of them aims at bringing out the precise model of party (called “parliamentary party”), conceptualized by the Liberals’ idea of constitution, while also highlighting how this party was formed, what its features were, and what different possible declinations the Italian public law finally offered for it, all in the light of the extraordinary methodological change which the country’s law went through, because of V.E. Orlando, from the 1880s onwards. In the second part of the volume, on the other hand, an attempt was made to describe the violent impact that this model of party encountered when the entire constitutional culture of the Liberals had to deal with social and political (and, one could say, anthropological) changes which were typical of the 20th century.