Attachment theory has been extremely successful at stimulating research on the formation and quality of emotional bonds between relationship partners, and on the complex interplay between individual-level and relationship-level processes in all phases of the lifespan. In this chapter, we review and assess some of the many empirical findings and propose integrative ideas concerning both normative and individual-difference aspects of personal relationships in adulthood. First, we present our model of the activation and psychodynamics of the attachment behavioral system in adulthood and describe the intrapsychic and interpersonal manifestations of the sense of attachment security, as well as the regulatory strategies of hyperactivation and deactivation. Next, we present a systematic review of studies that have examined the implications of variations in attachment-system functioning for the formation and maintenance of dyadic close relationships. Specifically, we focus on the contribution of these variations to relational wishes and goals, attitudes toward intimacy and commitment, patterns of dyadic communication, responses to a partner’s negative and positive behaviors, the experience and management of relational conflicts, and the provision of effective care to a needy partner. Finally, we extend our theoretical analysis to other kinds of relationships, such as therapeutic relationships and relationships within groups.