In this chapter, we discuss recent empirical and theoretical advances that demonstrate how, why, and under what conditions interdependent relationships promote self-expansion (i.e., the cognitive reorganization of individuals’ self-concept due to the acquisition or augmentation of traits, perspectives, identities, and capabilities). In particular, we discuss ways in which engaging in self-expansion has the potential to not only enhance individual well-being but to also enhance close relationships. In the first section of the chapter, we review the broadening and deepening of research on the fundamental tenets of the self-expansion model. Specifically, we begin by identifying the defining characteristics of the self-expansion process, such as the underlying features of shared relational activities that foster self-expansion. We then explore cognitive and motivational antecedents of self-expansion seeking, particularly experiences that promote approach motivation and subsequent interdependence. Furthermore, we discuss the relational, behavioral, cognitive, affective, and physiological outcomes of the self-expansion process, and we consider how the outcomes of both relational and individual self-expansion shape expectations for relationships. In the second section of the chapter, we review interdependence-based extensions and applications of the self-expansion model. Specifically, we discuss additional self-concept changes that interdependent relationships can foster, including cognitive reorganizations that have deleterious intra- and interpersonal consequences. Additionally, we examine how self-expansion can occur in myriad contexts (e.g., through individual experiences, romantic relationships, friendships, the workplace, and intergroup interactions), and we explore novel applications and implications of self-expansion, such as reducing relationship conflict and intergroup prejudice. Finally, using the recent research in self-expansion as context, we discuss potential directions for future research.

In this chapter, the authors draw upon Abraham Maslow’s self-actualization theory, Eli Finkel’s suffocation model of marriage, and Arthur and Elaine Aron’s self-expansion model in the process of examining relationship maintenance among members of various cultural groups. A review of the literature on nationality as culture (following Goodwin) suggests limited support for the effects of a nation-level East–West dichotomy on mean levels of relationship maintenance behaviors (i.e., where such an effect exists, persons in Western nations sometimes engage in significantly higher levels of relationship maintenance behaviors than do persons in Eastern nations) and the effects of such a dichotomy on covariance between equity norms and relationship maintenance behaviors (i.e., where such an effect exists, within Western nations only, individuals are more likely to engage in relationship maintenance behaviors when they perceive their relationships as equitable rather than unequitable). However, the effects in question are not consistent and do not generalize to ethnic group differences in means or covariance involving relationship maintenance behaviors within Eastern or Western nations. Implications for studies that integrate cultural psychology with relationship science are discussed.