AbstractCriticism of development projects is widespread, and blame for disappointing results is cast in many directions. One line of criticism which has become quite strong in the recent development literature is that development projects are too top‐down and need to be more bottom‐up (e.g. Maguire, 1981). Projects should involve more participation by beneficiaries. In fact, some would argue that real development, by definition, must involve beneficiaries in their own improvement (e.g. Gran, 1983a,b). Without participation the people may benefit but not develop from a project. Thus participation has intrinsic value.As the recognition of the value of public, popular, beneficiary, or community participation has increased, so has the range of what is meant by participation. Some authors have expanded the concept to mean empowerment and capacity‐building, sometimes including institution‐building. In this paper we do not attempt to redefine participationper se.but aim instead to make an inventory of the principal concepts that have evolved in the literature so far, elicit a general model of participatory development projects, deduce the central implicit hypotheses from this literature on the relationship between participation and project effectiveness, and statistically test these hypotheses from the empirical evidence provided by AID'S series of 52 Impact Evaluation Reports. Our major question is how much does beneficiary participation contribute to project effect