This panel invites scholars to engage with a relatively neglected idea of 20th century constitutional studies: the material constitution. As an object of constitutional study, this notion has been engaged in a systematic way only by legal institutionalists of the first wave (Heller, Smend, Mortati, Schmitt of the 30s) and, in a different tradition, by a legal positivist like Hans Kelsen. The main intention of this panel is to unearth this notion and to begin an exploration of its epistemic potential. This will be done by examining how the notion has been understood by legal positivists and by sociological constitutionalism. Moreover, two concrete case studies (Mexico and Chile) will illustrate how the notion has been used by the judiciary and the political system.