This thesis is about the relationship between research, data and the population problem in India between 1938 and 1974. It argues that the research practices and the data collected by demographers and social scientists in India are crucial to understanding how the population problem was framed, understood, and acted on. New kinds of research such as sample surveys, and knowledge attitude and practice (KAP) surveys were instrumental in constructing India as an overpopulated country in the twentieth century, as well as in furnishing India with the means to use and challenge this label by the 1970s. Many of the arguments made about the history of population control in India have focused on the role of the international network of population control experts in shaping the policies implemented by the Indian Government. This historiography has stressed the importance of contraception and of American expertise. This thesis re-frames this narrative by focusing on social science research and researchers as they worked in and on India. It examines the importance of behavioural approaches to family planning and population control, and their role in shaping how the population problem was understood and acted on. It revisits the importance of arguments about development, modernization, and fertility, focusing on the importance of different developmental models and their impact on population policy in the post-colonial period. It charts the connections between research and policy, exploring how they raised new questions about the empirical reality of the population problem, about the proper way to measure and understand it, and ultimately, explores the relationship between the state, statistics and individuals.