This groundbreaking study investigates theories of Islamic constitutionalism as expressed and implemented throughout the history of Islam. To achieve this, it first traces the roots of caliphate embedded within the seminal legal and political works of classical and modern Muslim thinkers. In its concluding chapters, the study maps out and discusses the subsequent transition of Islamic and Muslim governance into twentieth-century approaches to constitutionalism. Longo's resourceful and meticulous approach sheds new light on constitutionalism within the contemporary Muslim world and how it continues to be informed by, or departs from classical theories of Islamic and Muslim governance.