The paper tries to explain why social capital has become more important in the current organization of the economy. The search for flexibility and quality production, in the context of a growing globalization, enhanced the role of cooperation among both individual and collective actors at a local level. However, it seems necessary to consider social capital as a network of social relations rather than a mere cooperative culture based on shared values. This view allows to better understand not only the positive effects of social capital for a self-sustained local economic development, but also the possible negative consequences in terms of rent-seeking, collusion, or even criminal economy. The paper points to the crucial role of political factors - of the "embedded autonomy" of political action - in favoring a positive role of social capital in local economic development, as showed by some cases of regional development in Europe, or by some success stories in East Asia. This may open up new possibilities for more effective policies aimed at fostering local economies in the era of globalization.