As medicines were imported, distributed, marketed, consumed, and even eventually produced in Vietnam, under the conditions created by colonial health policies and regulation, as well as by dynamic private therapeutic markets and changing practices of health consumption and care, they became, in various ways, colonial medicines. In other words, by circulating in colonial Vietnam, modern medicines were transformed in terms of their forms, meanings, effects, and identities. This transformation is a core topic of this book. Yet even outside Vietnam, and notably in the French metropole, the very notion of what a medicine was – its form and appearance, how and by whom it should be made and sold, how it should be regulated and advertised, prescribed, and consumed, how it should be owned, and what it should do – changed profoundly, albeit gradually, between the mid-nineteenth and mid-twentieth centuries.