Internal boundaries between information systems divisions have traditionally caused friction and frustration, and negatively affected IT staff job satisfaction. Adopting open source development principles and processes within a corporate environment, what has been labeled ‘inner source,’ is now part of a larger management strategy to break down silos and promote innovation, collaboration, cooperation and communication across divisions of an organization. In this article we argue that inner source emphasizes the importance of relationships between developers and teams interacting across intra-organizational boundaries. We posit that inner source helps to create social capital, which in turn links to higher levels of job satisfaction. We use a sequential mixed-methods approach to test a theoretical model by combining quantitative survey data collected at one IT organization with qualitative data based on interviews with professionals from six organizations that adopted inner source. The results suggest that employees who participate in inner source projects develop more social interaction ties with others and have higher levels of shared understanding of software projects. Furthermore, we confirm that social interaction ties and a shared understanding link to a higher degree of trust. Finally, this study provides evidence that social capital mediates the link between participation in inner source and job satisfaction, implying that an inner source strategy can offer benefits to organizations. Enriched with the findings from the qualitative interviews, we then identify a number of implications for managers.