Over the past decade attachment theory has undergone an intense expansion of both its original scientific foundations as well as its applications to clinical work. Bowlby's original description occurred during a period of behaviorism and an emphasis on the strange situation and secure base behaviors, which then gave way to a dominance of cognition and an emphasis on attachment narratives and reflective capacities. We will argue that in line with Bowlby's fundamental goal of the integration of psychological and biological models of human development, the current interest in affective bodily-based processes, interactive regulation, early experience-dependent brain maturation, stress, and nonconscious relational transactions has shifted attachment theory to a regulation theory. This emphasis on the right brain systems that underlie attachment and developmental change has in turn forged deeper connections with clinical models of psychotherapeutic change, all of which are consonant with psychoanalytic understandings. Modern attachment theory can thus be incorporated into the core of social work theory, research, and practice.