In the early 2000s, a new systems theory, multisystemic therapy (MST), has been applied to family therapy and is practiced most often in a home-based setting for families of children and adolescents with serious emotional disturbances.

MST is frequently referred to as a "family-ecological systems approach" because it views the family's ecology, consisting of the various systems with which the family and child interact (for example, home, school, and community).

Several clinical studies have shown that MST has improved family relations, decreased adolescent psychiatric symptoms and substance use, increased school attendance, and decreased re-arrest rates for adolescents in trouble with the law.

In addition, MST can reduce out-of-home placement of disturbed adolescents.