While much current research on political Islam revolves around militant Islamism, the genesis of this ideology remains little understood. A System of Life is a pioneering examination of the earliest attempt at a systematic outline of Islamist ideology, namely that proposed in the 1930s and early 1940s by the renowned Indo-Muslim intellectual Sayyid Abu’l-A’la Mawdudi. Hartung reconstructs his thought in the light of the competing ideologies at play at the time, especially his claim to recast Islam as an all-comprehensive, self-contained and inner-worldly system of life. His analysis is embedded in an understanding of the history of ideas that assumed increasingly global dimensions through colonial encounters. By showing how Mawdudi — depicted as a major protagonist of this development — attempted to align elements of Western philosophical thought with selected traditional Islamic ideas and concepts, ‘Islamism’ is established as an Islamic contribution to a universalistic notion of modernity. Alongwith offering a detailed portrayal of Mawdudi’s system of thought, Hartung also discusses the reception and modification of his ideas in the Middle East, predominantly among intellectuals of the Egyptian Muslim Brotherhood, and among their imitators in postcolonial South Asia.