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 theimposing 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.