This paper summarizes 15 years of empirical research at various spatial levels on social capital and economic performance. On the firm level, results are unambiguous: there is strong evidence of the impact of social capital on firms' performance. However, the results become less clear for spatial units with a large number of anonymous actors. The contradictory results of studies on national and regional levels can be explained in part by insufficient measures of the main component parts of social capital: social networks and the norms and values distributed among them. To develop measures for values like creativity, entrepreneurship and tolerance, and to find better measures for social networks, are the main challenges to future research.