During the late 19th century, opium was integral to European colonial rule in Southeast Asia. The taxation of opium was a major source of revenue for British and French colonizers, who also derived moral authority from imposing a tax on a peculiar vice of their non-European subjects. Yet between the 1890s and the 1940s, colonial states began to ban opium, upsetting the very foundations of overseas rule—how did this happen? Empires of Vice traces the history of this dramatic reversal, revealing the colonial legacies that set the stage for the region’s drug problems today. Diana Kim challenges the conventional wisdom about opium prohibition—that it came about because doctors awoke to the dangers of drug addiction or that it was a response to moral crusaders—uncovering a more complex story deep within the colonial bureaucracy. Drawing on a wealth of archival evidence across Southeast Asia and Europe, she shows how prohibition was made possible by the pivotal contributions of seemingly weak bureaucratic officials. Comparing British and French experiences across today’s Burma, Cambodia, Laos, Malaysia, Singapore, and Vietnam, Kim examines how the everyday work of local administrators delegitimized the taxing of opium, which in turn made major anti-opium reforms possible.