Erikson proposed that the task of adolescence and young adulthood was to define the self by answering the question, 'Who am I?'. Following Erikson, this volume takes a developmental perspective on this question of identity, one characterized by a focus on developing a sense of the self that is temporally continuous and unified across the different life spaces that individuals inhabit. There have been many advances in theory and research on identity development since Erikson's writing more than 50 years ago, and the time has come to consolidate our knowledge and set an agenda for future research. This handbook is poised to represent a turning point in the field of identity development research.