Abstract
The evolution of the study of identity development is traced from Freud's early writings to Erikson's extrapolations and theoretical expositions, Marcia's empirical operationalization, and finally to 6 alternative theories that have been introduced since 1987 (Berzonsky, Grotevant, Waterman, Kurtines, Adams, and Côté. The issues of measurement and intervention, which have been crucial to the evolution of identity as a researchable construct, are also reviewed. The alternative theories are conceptualized as addressing aspects of Erikson's work that were not addressed by Marcia's identity status model. To facilitate the broadening of identity theory to include more of Erikson's ideas, taxonomies for understanding relations among the alternative theories, and a system for integrating them, is introduced. Finally, suggestions for the development of future identity theory and research are offered.