This book brings together philosophers, social psychologists and social scientists to approach contemporary social reality from the viewpoint of solidarity. It examines the nature of different kinds of solidarity and assesses the normative and explanatory potential of the concept. Various aspects of solidarity as a special emotionally and ethically responsive relation are studied: the nature of collective emotions and mutual recognition, responsiveness to others' suffering and needs, and the nature of moral partiality included in solidarity. The evolution of norms of solidarity is examined both via the natural evolution of the human "social brain" and via the institutional changes in legal constitutions and contemporary work life. This text will appeal to students, scholars, and anyone interested in the interdisciplinary topic of social solidarity.