From the 1950s onwards, fear of a population explosion in so-called underdeveloped countries spread in the West. A rapidly increasing number of population experts aimed to address this perceived threat through family planning, new contraceptive methods, and sexual education. Teresa Huhle demonstrates how, in Colombia, sociological, demographic, and medical knowledge was developed as part of these efforts, significantly shaping societal debates around family, gender, sexuality, and health—debates that negotiated nothing less than the design of a modern and developed country with responsible citizens.