In this work, Nan Lin explains the importance of using social connections and social relations in achieving goals. Social capital, or resources accessed through such connections and relations, is critical (along with human capital, or what a person or organization actually possesses) to individuals, social groups, organizations, and communities in obtaining their objectives. This book places social capital in the family of capital theories (the classical and neo-capital theories), articulates its elements and propositions, presents research programmes, findings and agenda, and theorizes its significance in various moments of interactions between individual actions and social structure (for example, the primordial groups, social exchanges, organizations, institutional transformations, and cybernetworks). Nan Lin introduces a theory that forcefully argues and shows why it is who you know, as well as what you know that makes a difference in life and society.