Through a focused and systematic examination of late medieval scholastic writers – theologians, philosophers and jurists – Joseph Canning explores how ideas about power and legitimate authority were developed over the ‘long fourteenth century’. The author provides a new model for understanding late medieval political thought, taking full account of the intensive engagement with political reality characteristic of writers in this period. He argues that they used Aristotelian and Augustinian ideas to develop radically new approaches to power and authority, especially in response to political and religious crises.