Attachment theory is a psychological theory that attempts to understand a specific aspect of interpersonal relationships. Attachment theory does not deal with every aspect of human relationship, but how people respond when relationships hurt, when they are separated from loved ones, or perceiving a threat to loved ones. The single most important aspect of attachment theory seeks to show how an infant must develop a relationship with at least one primary caregiver in order to learn how to effective regulate feelings.
In this understanding, attachment refers to the biological instinct whereby a child seeks proximity to an attachment figure when he or she perceives a threat. The child anticipates that the attachment figure will remove the threat. Pre-attachment occurs during the first six months, when infants learn to discriminate between familiar and unfamiliar adults, and become responsive to caregivers. Between six months and two years, the child develops organized behavioral attachment towards the caregiver in order to achieve emotional security.
Toddlers who are securely attached to parents or caregivers will learn to, and be comfortable with, exploration while the caregiver is present, will engage with strangers, and become visibly upset when the caregiver departs. Children who develop ambivalent attachment will not explore become wary of strangers, even in the presence of parents.