Donors and governments increasingly seek to deliver development projects through community-based organizations such as self-help groups (SHGs), but little is known about the effectiveness of such arrangements. This article briefly summarizes hypotheses regarding the effectiveness of interventions using SHGs and presents the results of an evidence review on the impacts of interventions delivered through SHGs on health, finance, agriculture and empowerment outcomes in South Asia and sub-Saharan Africa. Though the impacts of SHG-based interventions are generally positive, the evidence base is limited and does not generally test whether alternative delivery mechanisms might be more effective.