Global regulatory agencies have licensed vaccines to prevent at least 25 infectious diseases. Historically, however, new vaccines typically became available in low- and middle-income countries years (often decades) after being introduced in high-income countries. More recent initiatives have narrowed this inequity, with well-documented positive impacts on health and survival in these vulnerable populations.  This White Paper discusses the World Health Organization’s Prequalification program, which has been a key contributor in overseeing the quality, safety, and suitability of vaccines used in national immunization programs.