Although 'loyalty' is in itself a relatively modern term, as a phenomenon it has long been recognised as a fundamental element of social relationships. The essays collected in this volume address the concept of loyalty as it was understood in the Middle Ages, exploring the theme of loyalty from three separate angles—the ties between individuals (such as marriage or feudal ties), the ties between individuals and groups (for example, the role of the individual in their wider family), and the ties between institutions and groups (such as monastic orders or guilds)—and questioning how, when, and why the phenomenon of loyalty first developed. This volume, which draws together contributions from leading historians, explores how loyalty was manifested, both in public and in private, in the medieval world. Covering topics as diverse as religious orders, royal courts, and funeral customs, the essays collected here explore the interplay between loyalty and love, friendship, obedience, and justice, and question how the value of loyalty functioned both in theory and in practice across a range of social spaces. Together, these articles offer a unique new perspective on medieval society and provide a framework that also promises to be fruitful for future research.