There are four phases of attachment during infancy: preattachment phase, attachment-in-making phase, clear-cut attachment phase, and formations of reciprocal relationships phase.

In the preattachment phase, which spans from birth to about age 6 weeks, babies' automatic reflexes, and activities such as grasping, crying, and rooting, will cause caregivers to want to attach to babies. Caregivers will feel needed and want to meet all their babies' needs. However, at this time, babies are not yet attached to any one caregiver, and they do not care if they're held or cared for by strangers. However, some research suggests that babies know their mothers' voice and unique scent from birth and recognize their mother that way. During this phase, babies may sometimes respond to social interaction from caregivers; at other times, babies may not readily respond at all. Babies can smile automatically in response to voice and touch from birth to about age 2 months, which encourages caregivers to interact with them. This interaction will increase their mental, emotional, and social growth and learning.

During the attachment-in-making phase, which spans from about age 6 weeks to about 6 to 8 months, babies begin to react differently and more quickly to primary caregivers than strangers, and they start building trust in caregivers to fulfill needs. They are slowly starting to count on their caregivers to take care of them. However, infants at this stage are still not distressed at being separated from particular caregivers. During this stage, they continue to make gestures and actions that help encourage caregivers to bond with them. Babies begin making eye contact around age 2 months, and can smile intentionally between ages