I present a historical study of the role played by the World Health Organization and UNICEF in the emergence and diffusion of the concept of primary health care during the late 1970s and early 1980s. I have analyzed these organizations' political context, their leaders, the methodologies and technologies associated with the primary health care perspective, and the debates on the meaning of primary health care. These debates led to the development of an alternative, more restricted approach, known as selective primary health care. My study examined library and archival sources; I cite examples from Latin America.