Change in the adult identity of 155 participants from the Intergenerational Study, Institute of Human Development, was examined across a period of 24 years, and was related to theory-based life experiences and the use of defense mechanisms. The results indicated an increase in Achieved, Moratorium and Foreclosed Identity, and a decrease in Diffusion. As was expected from previous research and theory, identity change in middle adulthood and late middle age was predicted by use of the defense of identification. In addition, life experiences in the areas of work, marital and family relationships, social network, and political orientation were significantly related to identity and identity change. For both defenses and life experiences, IQ significantly moderated the predictions of identity change. (C) 2003 Elsevier Inc. All rights reserved.