This thesis investigates how and why bishops began to employ specially empowered deputies (i.e. vicars general) to run their dioceses on their behalf, particularly in the course of the thirteenth century. It seeks to discover, in a particular sample, how much administration was effected by means of deputies in the period, the purposes for which deputies were employed, and more generally the consequences of their employment on the role of the bishop in medieval society. Structurally, the thesis is divided into three main sections. The first is a detailed case study of a particular bishop of Winchester and the vicarial administration of his diocese during an absence of some fifteen months, between January 1322 and April 1323. Having established the nature of the phenomenon, the next section, comprised of two chapters, explores the foundations in canon and Roman law that enabled bishops to appoint others to act in their names. Finally, a third section is formed by another case study of a different type. Drawing upon an accompanying edition of acta performed by episcopal deputies in the diocese of Lincoln in the period from 1186 to 1272, it analyses the development of the deputies’ ‘office’ in the formative first century of its existence, from the earliest known instances under St. Hugh of Avalon (r. 1186-1200) until the final vicariate of the episcopate of Richard Gravesend (r. 1258-1279). In addition to analysing this administrative and legal evolution, the final section also considers the circumstances behind the appointment of each deputy, that is, the various reasons why the bishop was incapable of acting himself. The results of this study have important implications for our understanding of the influence of Roman law in the middle ages, assumptions about medieval bureaucratisation, and changes in the nature of the diocese and episcopal office in the late twelfth and thirteenth centuries.