Although the development field generally considers social and behavior change interventions essential parts of quality health programs, lack of synthesized information on costs and effectiveness means that decision-makers under-appreciate and under-fund social and behavior change efforts. This business case uses evidence to answer questions about the effectiveness, cost, cost-effectiveness, and return on investment from social and behavior change efforts. To develop this family planning social and behavior change business case, nearly 200 studies were evaluated. All USAID strategic priorities for global health—preventing child and maternal deaths, controlling the HIV/AIDS epidemic, and combating infectious diseases—employ social and behavior change approaches to varying degrees. This is the first in a planned series of complementary, health area-specific business cases