This book offers a comprehensive review of how social relationships foster well-being and health at various stages of life. By explicitly focusing on three main stages of a person's life, this book guides the reader through the influences of social relationships on the quality of life in adolescence, adulthood, and old age. Moreover, the book investigates the causal, very often psychological, mechanisms linking social relationships with quality of life. Building on the works of economists, sociologists, communication experts, psychologists and public health experts, this book provides an in-depth description of the possible mechanisms that make social relationships pivotal in people's life.