John of Gaunt (1340-1399) was arguably the most powerful nobleman in late medieval England, and his affinity--his household servants, indentured retainers, and estate officials--formed one of the crucial bases of his power. This book examines the genesis, composition, and actions of the imposing Lancastrian affinity in detail, and emphasizes the extent to which even a great magnate like Gaunt was constrained in the policies he pursued by the actions and expectations of his followers.