Although it provides the only indicators of the prevalence of mental disorders in the population, the history of psychiatric epidemiology is not well known. Moreover, epidemiology had a huge impact on global mental health policies after the foundation of the WHO (1948). The first goal of this project is to identify the scientific actors and communities who were active in the field of psychiatric epidemiology, starting with the local production of knowledge in Germany. Using epidemiological literature and archival documents held by the Max-Planck-Gesellschaft (MPG), the project is creating a prosopography of the researchers who contributed to the development of psychiatric epidemiology between 1954 and the present. The second objective of this historical analysis is to reconstruct scientific networks in a transnational perspective, considering different levels of scale. Psychiatric epidemiology at the MPG depended on researchers who were partly trained overseas before being appointed to high-ranking positions in Germany. Thus, the focus is on describing how epidemiological instruments—questionnaires and other artefacts—circulated between different scientific communities and were appropriated in a context of increased knowledge transfers during two key periods, the years of the Wirtschaftswunder, and the period after the fall of the Berlin Wall. Other questions raised relate to the development of psychiatric epidemiology as a history of the expertise on which national health agencies, international agencies, and NGOs launched policies for the prevention of chronic disorders, a major change in health planning after 1945. What are the connections between epidemiological studies and the planning of the health care in the context of Western welfare states? Do the questionnaires used around the world for international surveys have a history? What impact does translation, adaptation, and appropriation of questionnaires have on the local scientific investigation? In addition to Germany, the research project will address case studies in in France, UK, Portugal, Brazil, and North America.