Attachment theory is developmental psychology, a theory concerning the relationship between humans. The psychiatrist and psychoanalyst John Bowlby formulated this theory. This theory focuses on relationships and bonds between people, like between parent and child and between Romantic partners. Bowlby believed that the earliest bonds formed by children with their parents or caregiver have a tremendous impact throughout life. He also suggested that attachment serves to keep the infant close to the mother,  hence improving their chances of survival.

Throughout history, children who maintained proximity to an attachment figure were more likely to receive comfort and protection, and thus more likely to survive to adulthood. In short, attachment theory is that primary caregivers who are available and responsive to an infant's needs allow the child to develop a sense of security. The infant learns that the caregiver is dependable, which creates a secure base for the child to then explore the world. Based on the observation of Schaffer and Emerson there are four distinct phases of attachment:

- Pre-Attachment Stage, from birth to three months, infants don't show any particular attachment to a specific caregiver. The infant's signals, such as crying and fussing, naturally attract the attention of the caregiver and the baby's positive responses stimulate the caregiver to stay close.

- Indiscriminate Attachment, between six weeks of age to seven months, infants start to show preferences for primary and secondary caregivers. Infants develop trust that the caregiver will respond to their needs. While they still accept care from others, infants start differentiating between familiar and unfamiliar people, responding more positively to the primary caregiver.

- Discriminate Attachment, at this point, from about seven to eleven months, infants show a strong attachment and preference for one specific person. They will protest when separated from the primary attachment figure (separation anxiety), and begin to display anxiety around strangers (stranger anxiety).

- Multiple Attachments, after approximately nine months, children begin to form strong emotional bonds with other caregivers beyond the primary attachment figure. This often includes a second parent, older siblings, and grandparents.

Factors that influence attachment include the opportunity for attachment where children who don't have a primary caregiver, like those who were raised in orphanages, may fail to develop the sense of trust needed to form an attachment. And the second factor is quality caregiving, which is a vital factor, it is when caregivers respond quickly and consistently to the child, thus they learn that they can depend on people who are responsible for their care.

There are four patterns of attachment, including:

1- Ambivalent attachment: These children become extremely distressed when a caregiver leaves. And due to poor caregiver availability, these children cannot depend on their primary caregiver to be there when they need them.

2- Avoidant attachment: Children with an avoidant attachment tend to avoid caregivers, showing no preference between a caregiver and a stranger. This attachment style might be a result of abusive or neglectful caregivers. These children who are punished for relying on a caregiver will learn to avoid seeking help in the future.

3- Disorganized attachment: These children display a confusing mix of behavior, seeming disoriented, or confused. They may avoid or resist the parent. Lack of a clear attachment pattern is likely linked to inconsistent caregiver behavior. In such cases, parents may serve as both a source of comfort and fear, leading to disorganized behavior.

4- Secure attachment: Children who can depend on their caregivers show distress when separated and joy when reunited. Although the child may be upset, they feel assured that the caregiver will return. When frightened, securely attached children are comfortable seeking reassurance from caregivers. This is the most common attachment style.

Children who are securely attached as infants tend to develop stronger self-esteem and better self-reliance as they grow older. These children also tend to be more independent, perform better in school, have successful social relationships, and experience less depression and anxiety. Although attachment styles portrayed in adulthood aren't necessarily the same as those seen in infancy, early attachments can have a serious impact on later relationships. Adults who were securely attached in childhood tend to have good self-esteem, strong romantic relationships, and the ability to self-disclose to others.