Conclusions: Infant attachment is a multipurpose behavioral system essential to social animals. During infancy patterns of behavior are established on which other long-term relationships are built. Originating in the infant’s protection, the primary purpose of attachment soon became to support brain development. The establishment of homeostasis of physiological systems, social and emotional development and learning are other functions. Infant attachment is found to some degree in all mammals and is greatly expanded in humans. Attachment is a behavioral system that is present at birth but that must be activated and developed.