This book sets out unique findings on whether social capital influences health and health inequalities in European welfare states. Drawing on cross-national data from the European Social Survey (ESS) as well as Swedish national survey data and registers, the book develops a new theoretical definition of social capital that guides the books empirical studies. The findings suggest that welfare state generosity is a decisive factor for social capital and that social capital is of significance for health inequalities both between and within European welfare states. The book also discusses the potential dark sides of social capital and examines evidence of circumstances in which social capital has negative health externalities.