The World Health Organization's post-World War II work on the epidemiology and classification of mental disorders and its vision of a "world psyche." In 1946, the World Health Organization undertook a project in social psychiatry that aimed to discover the epidemiology and classification of mental disorders. In Mad by the Millions, Harry Y-Jui Wu examines the WHO's ambitious project, arguing that it was shaped by the postwar faith in technology and expertise and the universalizing vision of a "world psyche." Wu shows that the WHO's idealized scientific internationalism laid the foundations of today's highly highly metricalized global mental health system.