The aim of this essay is to analyse some traits of the Weimar Constitution of 1919 through the eyes of Hermann Heller, one of the most eminent exponents of the German public law doctrine of the Twentieth century. Indeed, given the close link between the political passion and the scientific work of this jurist, Heller’s contribution cannot be understood only retracing his scientific production, being also the result of his political and social struggles. In particular, there will be focused on the juridical-philosophical implications of Heller’s thought concerning the nature and form of the Weimar Constitution as well as the concept of State and the related critical points, nowadays crucial for the debate in the fields of legal theory and history of constitutional law.