Book excerpt: Social identity research has transformed psychology and the social sciences. Developed around intergroup relations, perspectives on social identity have now been applied fruitfully to a diverse array of topics and domains, including health, organizations and management, culture, politics and group dynamics. In many of these new areas, the focus has been on groups, but also very much on the autonomous individual. This has been an exciting development, and has prompted a rethinking of the relationship between personal identity and social identity - the issue of individuality in the group. This book brings together an international selection of prominent researchers at the forefront of this development. They reflect on this issue of individuality in the group, and on how thinking about social identity has changed. Together, these chapters chart a key development in the field: how social identity perspectives inform understanding of cohesion, unity and collective action, but also how they help us understand individuality, agency, autonomy, disagreement, and diversity within groups. This text is valuable to advanced undergraduate and postgraduate students studying social psychology where intergroup relations and group processes are a central component. Given its wider reach, however, it will also be of interest to those in cognate disciplines where social identity perspectives have application potential.