Theorizing has focused on individuals' self-representations as a psychological resource for coping with life stress and developmental challenges in adulthood. Many of the prominent theories have conceptualized self-representations with regard to specific social contexts (e.g., role-specific selfrepresentations) and have examined specific structural organizations of the self-concept with regard to psychological adjustment. This article describes research on the associations between self-concept structures and psychological well-being in adulthood. Specific emphasis is given to the feature of self-concept differentiation (SCD). Most research suggests that a high level of SCD tends to indicate self-fragmentation and tends to be associated with poorer adjustment and psychological well-being. Findings from a daily diary study with adults of all ages are reported showing that different levels of SCD were in a consistent and meaningful way related to the daily endorsement of positive and negative self-attributes. Daily self-representations, in turn, were significantly related to individuals' level of daily negative affect and to intra-individual variation in negative affect. These findings suggest that SCD may exert its effect on adjustment and psychological well-being through specific ways of processing self-related information.The last two decades have seen important extensions of self-concept theory into research on adult development and aging (Brandtstädter & Greve, 1994;Filipp & Klauer, 1986;Markus & Herzog, 1991). In particular, theorists have focused on individuals' self-representations as a psychological resource for coping with the challenges of adulthood and old age (Brandtstädter & Greve, 1994;Freund & Smith, 1999;Greve & Wentura, 2003). 1 Many of these conceptualizations have focused on adults' self-representations with regard to specific social contexts (e.g., role-specific self-representations) and have examined the associations of different structural organizations of contextualized self-representations with different indicators of psychological adjustment (Campbell, Assanand, & DiPaula, 2003;Kling, Ryff, & Essex, 1997;Linville, 1987;Showers, Abramson, & Hogan, 1998). This article has three major parts. First, we will review the theoretical and empirical reasons that have served as background for studying contextualized self-representations in adulthood. Second, we will review research focusing on the associations between different self-concept organizations and indicators of psychological adjustment. In this review, we will highlight only some of the major findings with regard to certain self-concept organizations and will focus specifically on the associations of self-concept differentiation (SCD) and measures of psychological well-being. Third, we will present findings from cross-sectional studies and from a daily diary study examining the effect of SCD and daily self-representations on daily affect.Correspondence concerning this article should be addressed to Manfred Diehl, Human Development...