In psychologythe theory of attachment can be applied to adult relationships including friendships, emotional affairs, adult romantic or platonic relationships and in some cases relationships with inanimate objects " transitional objects ".
Investigators have explored the organization and the stability of mental working models that underlie these attachment styles. They have also explored how attachment impacts relationship outcomes and how attachment functions in relationship dynamics. Mary Ainsworth and John Bowlby founded modern attachment theory on 4 types of attachment styles of children and their caregivers. Children and caregivers remained the primary focus of attachment theory for many years.
Then, in the late s, Cindy Hazan and Phillip Shaver applied attachment theory to adult relationships. For example, romantic or platonic partners desire to be close to one another. Adults feel comforted when their attachments are present and anxious or lonely when they are absent. Romantic relationships, for example, serve as a secure base that help people face the surprises, opportunities, and challenges life presents. Similarities such as these led Hazan and Shaver to extend attachment theory to adult relationships.
Relationships between adults differ in many ways from relationships between children and caregivers. The claim is that the core principles of attachment theory apply to both kinds of relationships. Investigators tend to describe the core principles of attachment theory in light of their own theoretical interests.
Their descriptions seem quite different on a superficial level. For example, Fraley and Shaver  describe the "central propositions" of attachment in adults as follows:. Compare this with the five "core propositions" of attachment theory listed 4 types of attachment styles Rholes and Simpson: While these two lists clearly reflect the theoretical interests of the investigators who created them, a closer look reveals a number of shared themes.
The shared themes claim that:. No doubt these themes could be described in a variety of ways and other themes added to the list. Regardless of how one describes the core principles of attachment theory, the key insight is that the same principles of attachment apply to close relationships throughout the lifespan.
The principles of attachment between children and caregivers are fundamentally the same as the principles of attachment between adults. Adults are described as having 4 attachment styles: Secure, Anxious-preoccupied, Dismissive-avoidant, and Fearful-avoidant. The secure attachment style in adults corresponds to the secure attachment style in children.
The anxious—preoccupied attachment style in adults corresponds to the anxious-ambivalent attachment style in children. However, the dismissive-avoidant attachment style and the fearful-avoidant attachment style, which are distinct in adults, correspond "4 types of attachment styles" a single avoidant attachment style in children. The descriptions of adult attachment styles offered below are based on the relationship questionnaire devised by Bartholomew and Horowitz  and on a review of studies by Pietromonaco and Barrett.
There are several attachment-based treatment approaches that can be used with adults.