The importance of community in primary health care (PHC) is evident in the role of community participation and in the types of programs that are routinely implemented (community health-worker [CHW] programs, community clinics, community–based disease-control programs). Few health care providers and program administrators, however, have considered the meaning of community. Instead, they frequently impose their own definition of community and assume that it corresponds to local realities. This is problematic because target populations may have different ideas about what a community is and how it functions. When disparate ideas of community exist, they can affect the implementation of PHC programs, leading to low rates of acceptance, participation, and utilization. Using two examples, a community clinic in El Alto, Bolivia, and a CHW program in Rio Bronco, Brazil, this article discusses some of the problems that arise when local definitions of community do not correspond to programmatic definitions.