Limited social capital poses a critical bottleneck for sustainable rural development. Despite vast investment, development interventions focused on preserving the biodiversity of the Osa and Golfito region of Costa Rica have done little to address poverty or improve the well-being of local residents. The authors of the current study draw upon field research and data gathered from semi-structured interviews with 310 community leaders and rural residents to investigate the bottlenecks to development and how they are related to forms of social capital in the Osa and Golfito cantons in Costa Rica. Specifically, we draw upon the distinction of bonding, bridging, and linking forms of social capital to characterize the nature of benefits from collective action in communities in Osa and Golfito. The data suggest that the lack of bridging and linking forms of social capital may explain the region's persistent development challenges and may thus indicate where development-related investments are most likely to bear fruit.