The title of the thesis is The Role of the Prior of St John in Late Medieval England, c. l 300-1540. ' It investigates the unique political role of the Prior of St John in England between 1300 and 1540. It looks at changes in the Prior's public roles over time, with reference to particular moments when individual Priors were senior political figures. It further examines changes in the English Priory and the resulting development of the Prior's role. It also investigates of the effect of events in the eastern Mediterranean and the ensuing consequences for the Hospitallers and Prior of England, analyses the relationship between the Prior's connections with powerful merchants and the appointment of several priors as treasurer of England, and explores of the loss of the order's political control of its estates to local gentry and aristocrats. Chapter 1, the introduction, includes the aims, hypothesis, international background, historiography and methodology. Chapter 2 covers the financial role of the Prior, examining the role played by the three Priors who became treasurers of England, and discusses the Prior as a source of finance for the crown. Chapter 3 looks at the military duties of the Prior in service to the crown. Chapter 4 considers the diplomatic aspect of the Prior's international role. Chapter 5 examines the Prior's political role in national politics, focusing on the development of his role in parliament, great council, and king's council. Chapter 6 treats the Prior and the secularisation of the order in England based on the extant English Hospitaller lease books between 1492 and 1539. Chapter 7, the conclusion, assimilates the information in the preceding chapters, commenting on and analysing the Prior's place in English society. The main conclusion is that the Prior became much more involved in the English political system during the late fourteenth and especially mid-fifteenth centuries than has previously been supposed. This thesis is the only in depth study of the Prior spanning later medieval England. This enables it to chart changes in the Prior's role that shorter studies on individual Priors (Prior Nablous, 1184-1190, Prior Malory, 1432-1440) cannot perceive. In addition, it is the only study to make extensive use of the English National Archives (Public Record Office), whereas other Hospitaller histories draw the bulk of their information from the Hospitaller archives on Malta or from printed primary sources. Furthermore, the study is unique in its concentration the Prior's service to the English crown and in its approach, viewing this service as beneficial, rather than contradictory to the Hospitallers' interests. For the above reasons, this thesis makes a significant contribution to our knowledge of late medieval history, crossing the boundary between `national' and crusading history.