"Attachment" has been viewed as the process by which the infant bonds to a caregiver and develops and maintains affiliative social relationships. Whereas past theories suggested that the neurobiological mechanisms that enable the infant to engage in regulated social interactions develop autonomously, the more current view is that the organization of cognitive and emotional systems that regulate social behavior depends on early caregiver-infant attachment. It is well known that disruption of caregiver-infant attachment produces abnormal behavior and increases or decreases the activity of different brain neurochemical systems in rhesus monkeys. Furthermore, it has been suggested that these effects might serve as a model for the etiology of some forms of human psychopathology. Current research indicates that caregiver privation alters the development of usual interrelationships among the activity of several neurochemical and neuroendocrine systems and alters basic cognitive processes. In line with the idea that the caregiver usually exerts a potent organizing effect on the infant's psychobiology, the long-standing effects of caregiver privation on behavior and emotionality are probably attributable to changes in multiple regulatory systems and cognitive-emotional integration rather than restricted effects on the activity of any specific set of neurochemical systems.