During the early nineteenth century, European nations began to contemplate cooperation in sanitary matters, starting a diplomatic process that culminated in the International Sanitary Conferences and the first laws on the control of infectious disease. This article examines the origins of these conferences and highlights certain features that have been neglected in existing scholarship. It argues that while commercial pressures were the main stimuli to the reform of quarantine, these were insufficient in themselves to explain why most European nations came to see greater cooperation as desirable. It places special emphasis on the diplomatic context and shows that the peace of 1815 produced a climate in which many European nations envisaged a more systematic and liberal sanitary regime.