All three theories have contributed to the concept of dependent personality disorder as defined by the Diagnostic and Statistical Manual of Mental Disorders (DSM) of the American Psychiatric Association.
Davis, historically, the concept of co-dependence "comes directly out of Alcoholics Anonymous, part of a dawning realization that the problem was not solely the addict, but also the family and friends who constitute a network for the alcoholic." The concept of codependency overlaps with, but developed in the mainstream independently from, the older psychoanalytic concept of the passive dependent personality which is attaching oneself to a stronger personality.
"Dependency" is well-established in psychological literature. Whereas early on psychoanalytic theory emphasized the oral character and structural basis of dependency, social learning theory considered a tendency to be acquired by learning and experience, and ethological attachment theory posited that attachment or affectional bonding is the basis for dependency.
Codependency can occur in any type of relationship, including family, work, friendship, and also romantic, peer or community relationships.
In a codependent relationship, the codependent's sense of purpose is based on making extreme sacrifices to satisfy their partner's needs.
Codependency is a type of dysfunctional helping relationship where one person supports or enables another person's drug addiction, alcoholism, gambling addiction, poor mental health, immaturity, irresponsibility, or under-achievement.