Soil erosion is an important contributor to the agricultural decline, poverty, and emigration which characterize rural Haiti today. The numerous soil conservation projects have often ignored indigenous knowledge, techniques and socio-cultural institutions and have not generally resulted in sustained conservation. Limited adoption rates have supported widespread assumptions that peasants were noncooperative, individualistic actors who required substantial external incentives for changing land use behavior. An alternate strategy was utilized in Maissade, Haiti, where peasants now cooperate to treat small, multiple-owner watersheds. Field research was conducted to understand the cooperative action and the socio-economic factors associated with participation ("e.g." cooperation) and defection. Study results indicate that approximately one-half of watershed landholders participate, and a majority of labor is contributed by persons who do not own land in the watersheds. Participants also regularly treat nonparticipant land, and land tenure status is independent of both landholder participation and structure placement. Indicators of landholder exposure to trans-boundary erosion and the potential to economically benefit are associated with participation while the realization of a direct benefit is not. Landholder wealth status is independent of participation though landholders are significantly more wealthy than non- watershed participants. Participation is also strongly associated with membership in farmer cooperatives and labor exchange groups, and the previous adoption soil conservation innovations. The findings challenge conventional wisdom concerning peasant behavior in Haiti and also suggest that support of indigenous cooperative institutions can facilitate the treatment of common environmental problems.