China's one-child policy is one of the largest and most controversial social engineering projects in human history. With the extreme restrictions it imposed on reproduction, the policy has altered China's demographic and social fabric in numerous fundamental ways in its nearly four decades (1979–2015) of existence. Its ramifications reach far beyond China's national borders and the present generation. This review examines the policy's social consequences through its two most commonly invoked demographic concerns: elevated sex ratio and rapid population aging. We place these demographic concerns within three broad social and political contexts of the policy—gender, family, and the state—to examine its social consequences. We also discuss the sociological consequences of the policy, by reflecting on the roles of science and social scientists in public policy making.