This chapter examines the birth control survey research conducted by population technocrats c.1947–60, and analyzes how this research resonated with government efforts to manage the emerging problem of “overpopulation” via fertility regulation. Focusing on the leading population technocrat Shinozaki Nobuo, this chapter depicts how human agency participated in the at times precarious relationship between policy and practice. It also shows how the epistemological framework inscribed in the scientific knowledge produced by the survey research, harmonized with the economic and political rationale that buttressed the post-WWII state’s reconstruction efforts. To illustrate this point, the chapter examines: (1) the evident absence of the category of race and (2) the categorization of data by region and the research participants’ socioeconomic status. For (1), it contends that, by maintaining silence on the question of race, the research consolidated an image of Japan’s population as ethnically homogeneous, which was becoming increasingly dominant political discourse during this period. The phenomenon (2), I argue, embodied the burgeoning developmentalist logic that explicitly portrayed reproductive practices in terms of a nation’s socioeconomic achievement. Together, these phenomena served to produce a certain knowledge of the Japanese population that was particularly compatible with post-WWII Japan’s reconstruction efforts.