Most research on entrepreneurial activities and institutions focuses on identifying certain relationships between formal and informal institutions and entrepreneurship across economies. In this study, we advance entrepreneurship research by examining how social capital as a characteristic of the institutional environment affects the relationship between formal and informal institutions and entrepreneurial activities, differentially, in developing and developed economies. Supporting institutional theory and social capital theory, the results from our sample of 39 countries from 2001 to 2014, which contains over 30,000 identified individuals, indicate that social capital has a stronger influence in the relations between institutions and entrepreneurship. In developing countries, this influence is greater in the relationship between property rights, access to credit, subjective insecurity, and entrepreneurial activity. In developed countries, the greater effect of social capital is on the relationship between corruption and entrepreneurial activity.