In response to a recent call for research on the effectiveness of faith-based organizations, this article synthesizes how effectiveness has been defined and measured in evaluation research of faith-based programs. Although evidence indicates that religion can have a positive impact on individuals' well-being, no prior comprehensive review exists of the literature on the effectiveness of faith-based social service programs. Adopting the systematic review method, the authors explore how researchers have conceptualized and operationalized effectiveness and faith. The authors identify trends and limitations across studies and conclude with implications for researchers and practitioners interested in examining and delivering faith-based social services. (Contains 1 table.)