This chapter begins by providing a background to Islamic law and constitutions in the Muslim world. The authors then present a classificatory scheme that outlines the different institutional design models for constitutional interpretation in Muslim countries. These include a secular model, an Islamic model, and a hybrid model, with different countries falling along a spectrum of variations. The chapter considers several case studies, such as Kuwait and Egypt for the secular model, Iran and Saudi Arabia for the Islamic model, and Malaysia, Afghanistan, and Pakistan for the hybrid model. The chapter concludes by highlighting the ways in which the political context and certain choices in constitutional drafting can foster one system or another along the spectrum.