The aim of this article is to study the relations between social capital (SC) and the result of the efforts made by poor groups to reduce their poverty and social exclusion. To this end, SC is defined as the ability to obtain benefits from networks of social relations. This definition is then applied to the analysis of rural organizations in Mexico and Central America. The authors conclude that SC is a key resource in the success of the projects of the poor groups analyzed. However, in order for this to occur, certain conditions have to be met such as the preservation of social cohesion, the ability to solve new problems and a favorable economic and political climate.