Crowds in the 21st Century presents the latest theory and research on crowd events and crowd behaviour from across a range of social sciences, including psychology, sociology, law, and communication studies. Whether describing the language of the crowd in protest events, measuring the ability of the crowd to empower its participants, or analysing the role of professional organizations involved in crowd safety and public order, the contributions in this volume are united in their commitment to a social scientific level of analysis. The crowd is often depicted as a source of irrationality and danger - in the form of riots and mass emergencies. By placing crowd events back in their social context - their ongoing historical and proximal relationships with other groups and social structures - this volume restores meaning to the analysis of crowd behaviour. Together, the studies described in this collection demonstrate the potential of crowd research to enhance the positive experience of crowd participants and to improve design, planning, and management around crowd events. This book was originally published as a special issue of Contemporary Social Science.