Nearly 100 years ago, the international community met in Shanghai to discuss the single largest drug problem the world has experienced, i.e., the Chinese opium epidemic. Prior to the 1909 Shanghai Opium Commission, national governments and state-sponsored monopolies had an active role in selling opium across national borders. The profits were enormous. Even a country the size of British India derived 14 percent of state income from its opium monopoly in 1880. The first international drug convention, the International Opium Convention of The Hague, was signed in 1912 and entered into force in 1915. This convention was designed to curb shipments of narcotic drugs that were not meant to be used for medical purposes. As of 1920, international drug control became part of the responsibilities assumed by the League of Nations. Three main conventions were developed in 1925, 1931, and 1936, which provided the foundation for the practical operations of the international drug control system. Significant progress occurred in curtailing the licit trade in narcotic drugs during this period. Following World War II, multilateral drug control came under the auspices of the United Nations. A number of protocols for improving the control system were established and signed, with the most far-reaching being the 1953 Opium Protocol. The international drug control efforts aimed at limiting the licit international trade in narcotic drugs to medical requirements. Controls were then expanded to cover manufacture and production of drugs and then trafficking in drugs in the late 1930s. Achievements and unintended consequences of the international drug control system are discussed. Extensive tables and figures and 358 notes