Introduction to special issue. This Special Issue includes articles first presented as papers at a two-day symposium held at the University of Waikato, New Zealand, in February 2011. The event was designed to highlight a large Royal Society of New Zealand Marsden-funded research project, and to showcase current scholarly work in the field of the colonial and postcolonial histories of medicine, with a focus on histories of insanity. We also included the themes of medical migration in New Zealand’s national history, the movement of medical ideas and personnel across empire, a close study of the uses of the term ‘neurasthenia’ in French-colonial Vietnam, and the relationship between place, plants, and health across South Asia and Australia in the nineteenth century.