You may be interested in a new resource we have on this topic published April 2020 Attachment theory in practice by Sally Wassell.

Defining attachment

Attachment theory involves the study of human relationships, especially early, formative relationships. The work of attachment theorists such as John Bowlby and Mary Ainsworth has thrown light on key aspects of the social development of children. However, like many words that derive from everyday language people sometimes use the term attachment to mean different things. The definition offered by Fahlberg:

“…an affectionate bond between two individuals that endures through space and time and serves to join them emotionally ”
— Fahlberg (1994)