Social capital, it is widely accepted, is beneficial to economic performance. How is social capital formed and how can it be measured? Why do different communities have different levels of social capital? Research at Bocconi University examined group formation – an important dimension of social capital relatively easy to measure – and asked: how does an individual join a group? If diversity within a community – such as degree of income inequality – influences individual incentives to join a group that may provide shared economic benefits, several questions arise. Does greater inequality lead to more or less group participation? As inequality deepens, who drops out – the poorer or the richer members? Is the drop out rate linked to rules of access? Does inequality affect group performance, and therefore access to social capital?