The subject of this thesis is the organisation of the Shia Imami Ismailis in Britain. Part I is concerned with certain background topics. Chapter 1 touches on the history of Ismailisia in general, including how it came to India, and on points of doctrine which can best be understood in this context. The next three chapters of part I consider respectively religious, administrative and financial aspects of Ismaili organisation in East Africa as it has been developed during the twentieth century. The last chapter in part I discusses in greater detail the role of the imam (Aga Khan) in promoting change among his followers. The relevance of some of these developments for settlement in Britain is suggested. The first chapter of part II (chapter 6) describes the pattern to Ismaili migration to Britain, and how the composition of this migration changed over the years. Something of the resultant social diversity among Ismailis in Britain is suggested in chapter 7, though here the emphasis is on diversity in terms of British social classifications. In chapter 8 some detailed case histories are set out in an attempt to bring out the altered significance of collective Ismaili organisation in Britain. At this point the question of exogamy is also considered. The Ismaili council in Britain, based on the London mosque, forms the subject of chapter 9; comparison with its East African counterparts argues the weakness of the British council, and some of the reasons are suggested. The concluding chapter 10 looks tentatively at the Ismaili migration to Britain in terms of the changing basis of community economic activity in East Africa in the light of the post-independence situation there, and also discusses the structure of the Ismaili organisation in Britain, examining the decline in collective organisation and the social fragmentation of Ismailis here