I n recent years, attachment theory (Bowlby, 1973, 1980, 1982, 1988), which was originally formulated to describe and explain infant-parent emotional bonding, has been applied –rst to the study of adolescent and adult romantic relationships and then to the study of group dynamics and intergroup relationships. In the present chapter we expand the theory as it applies to adults by discussing attachment-related processes involved in (1) the ways people think, experience, and cope with interpersonal conicts; (2) maladaptive forms of conict resolution within romantic and marital relationships; and (3) intergroup hostility and aggression. We will begin by presenting an overview of attachment theory and our theoretical model of the activation and psychodynamics of the adult attachment behavioral system (Mikulincer & Shaver, 2007a), along with an overview of some of the intrapsychic and interpersonal manifestations of the senses of attachment security and insecurity (attachment anxiety and avoidance). We will then focus on attachment theory’s characterization of individual differences in adaptive and maladaptive forms of experiencing interpersonal conicts and coping with them. Next, we will review –ndings concerning the ways attachment security and the major forms of insecurity affect various forms of conict resolution in close relationships. Finally, we will review recent –ndings concerning ways the senses of attachment security and insecurity (anxiety and avoidance) shape a person’s attitudes and behavior toward out-groups and reduce or intensify intergroup conict.