There is a surprising gap in the economic literature on social capital. First, we lack studies addressing the effects of social capital on those facets of development that can contribute in making growth more sustainable in the long run, like, for example, human development and social cohesion. Second, it is still unclear what type of networks may exert a positive effect on the different dimensions of development. In particular, the literature has not yet provided a rigorous assessment of the role of strong family ties, that are generally referred to as a form of bonding social capital causing backwardness. This paper investigates the relationship between the three types of social capital so far identified by the literature (i.e. bonding, bridging and linking), and the "quality" of economic development, as expressed by human development and an index of social well-being summarizing the state of health of urban ecosystems, public services, gender equality, and labour markets. Copyright 2008 The Authors. Journal compilation 2008 Blackwell Publishing Ltd.