Phase therapists are psychotherapists who have completed both the differentiation therapy course and the phase therapy course. Phase therapy was developed for children and adolescents with a relational disorder; differentiation therapy was developed for children with an attachment disorder. See the list of phase therapists.

Basis therapists are psychotherapists who have completed the basis therapy course. Basis therapy was developed for adults with a relational disorder. See the list of basis therapists.

Differentiation therapists are play therapists who have completed the differentiation therapy course. See the list of differentiation therapists.