This thesis represents the first full length study of the life and works of Dr George Cheyne (1672-1743). The introduction reviews earlier studies. The biographical content provides a substantial amount of new information derived from neglected printed sources and unrecorded archive material. An interdisciplinary approach is taken in an attempt to illustrate the close, if complex, connection between Cheyne's biography and the development of his medico-religious ideas. Particular attention is given to the role of Cheyne's engagement with Christian mysticism in shaping his promotion of notions of sensibility amongst the Georgian literati. There are ten chapters. Chapters one and two trace Cheyne's origins in Aberdeenshire, and his emergence at Edinburgh in 1700 as the controversial champion of the iatro-mathematical medical theories of Dr Archibald Pitcairne. An account of Cheyne's early years in England examines his mathematical collaboration with John Craige, and his failure to impress Newton with the publication of The Philosophical Principles of Natural Religion (1705). Chapter three examines Cheyne's crucial breakdown in 1704-6 and his rejection of 'Natural Religion' in favour of sentimental, pietism. It provides a detailed account of the unorthodox pietist sects (many with close links to the Continent), with whom Cheyne became associated. Chapter four analyses Cheyne's millenarianism: whilst the Camisard Prophets focused his interest on the relationship between nervous illness and spiritual illumination, his quietist-mysticism was a recoil from such 'Enthusiasm'. Chapter five argues that the enlarged Philosophical Principles of Religion: Natural and Reveal'd (1715), was a widely used academic textbook, despite the unorthodox 'mystical' colouring it gained when Cheyne attempted to reconcile a Newtonian theodicy with Behmenism.