It was only in the early twentieth century that China discovered that it had a population, at least if a population is understood not as a simple number of people but instead in terms of such features as variable levels of health, birth and death rates, age, sex, dependency ratios, and so on—as an object with a distinct rationality and intrinsic dynamics that can be made the target of a specific kind of direct intervention. In 1900, such a developmentalist conception of the population simply did not exist in China; by the 1930s, it pervaded the entire social and political field from top to bottom. Through a reading of a series of foundational texts in population and family reformism in China, this paper argues that this birth of the Chinese population occurred as a result of a general transformation of practices of governing, one that necessarily also involved a reconceptualization of the family and a new logic of overall social rationalization; in short, the isolation of a population–family–economy nexus as a central field of modern governing. This process is captured by elaborating and extending Foucault's studies of the historical emergence of apparatuses (dispositifs) into a notion of fields of governability. Finally, this paper argues that the one-child policy, launched in the late 1970s, should be understood not in isolation from the imposition of the “family-responsibility system” in agriculture and market reforms in exactly that period, but as part—mutatis mutandis—of a return to a form of governing that was developed in the first half of the twentieth century.