An important new contribution to the social sciences is the idea of social capital. Social capital consists of the resources that are embedded within people's social networks. Validated by empirical research, this book presents social capital research as an integrated theoretical research programme. The core of the programme consists of two hypotheses. The social capital hypothesis holds that those with better social capital are better able to realize their ends. And according to the investment hypothesis people invest in ties to the degree that these are instrumental in achieving their ends. The volume is organised into six parts, each addressing a fundamental issue in the research programme. First, the research programme is described. The second part presents the distribution of social capital among citizens of different societies using large-scale social surveys. In the third part experimental and simulation studies show how social capital is created. The fourth part analyses various returns of social capital such as educational and occupational attainment and performance at work. The fifth issue is how social capital should be measured in a more standardized way. And finally the new issue of social capital as a collective good is explored. Bringing together the work of a distinguished range of international contributors, this book explores the idea of social capital from a range of disciplinary perspectives and research methods and will be of essential interest to students and researchers of sociology.