This document discusses social capital in the context of regional innovation clusters in Korea. It defines social capital as the intangible resources embedded in social relationships and networks. Social capital is important for innovation clusters as the innovation process requires communication and cooperation. The document presents case studies of two Korean innovation clusters, in photonics and medical industries, and analyzes their social capital at the firm and regional levels. It finds that purposeful networks leading to innovation communities can accelerate cluster development, but more work is needed to strengthen social capital, such as through entrepreneurship and collaboration. Fostering innovation communities should be a focus of cluster policy.