This book examines the consequences of commercial and imperial expansion for British medicine between roughly 1660 and 1830. It pays particular attention to the development of medical ideas and practices in India and the British West Indies and their impact on medicine at home. The book argues that the tropical colonies were important sites of innovation and that the experience gained by practitioners working there transformed medical practice in ways which have not been fully appreciated. India, the West Indies, and other overseas outposts offered tremendous scope for those seeking to understand the nature of disease and to observe its effects in living patients and post‐mortem. Colonial hospitals also afforded many opportunities for trials of new drugs: not only new botanical remedies but also chemical therapies, some of which were pioneered in the colonies. It is argued that these opportunities bolstered a growing movement for reform in British medicine, with particular emphasis upon the importance of empiricism, experiment, and morbid anatomy. The book also ponders the relationship between reform in the medical arena and the politics of Dissent, as well as the impact of colonialism and commerce upon the professional environment in Britain. It shows how former colonial practitioners became increasingly influential in British medicine, tapping into fears about invasion by alien diseases, degeneration, and social change.