This thesis explores the relationship between social capital and innovation across 40 regions in the United States. Data is drawn from the Social Capital Community Benchmark Survey, compiled by the John F. Kennedy School of Government and the Saguaro Seminar, and the MicroPatent CD-ROM Database from the USPTO. Innovative activity is modeled as a function of knowledge stocks, human capital, four aspects of social capital, and other control variables across six industries over 38 years. The results suggest that certain manifestations of social capital, such as levels of trust and cooperation, consistently have a positive impact on innovative activity. Furthermore, communities with greater levels of cooperation and better-established networks innovate even more in the presence of previous local knowledge.