Attachment and bonding are evolved processes; the mechanisms that permit the development of selective social bonds are assumed to be very ancient, based on neural circuitry rooted deep in mammalian evolution, but the nature and timing of these processes and their ultimate and proximate causes are only beginning to be understood. In this Dahlem Workshop Report, scientists from different disciplines—including anthropology, psychology, psychiatry, and behavioral biology—come together to explore the concepts of attachment and bonding from diverse perspectives. In their studies they seek to understand the causes or the consequences of attachment and bonding in general and their different qualities in individual development in particular. They address such questions as biobehavioral processes in attachment and bonding; early social attachment and its influences on later patterns of behavior; bonding later in life; and adaptive and maladaptive (or pathological) outcomes. The studies confirm that social bonds have consequences for virtually all aspects of behavior and may be protective in the face of both physical and emotional challenges.