Family therapy is based on family systems theory, in which the family is viewed as a living organism rather than just the sum of its individual members. Family therapy uses systems theory to evaluate family members in terms of their position or role within the system as a whole. Problems are treated by changing the way the system works rather than trying to fix a specific member. Family systems theory is based on several major concepts

THE IDENTIFIED PATIENT The identified patient (IP) is the family member with the symptom that has brought the family into treatment. Children and adolescents are frequently the IP in family therapy. The concept of the IP is used by family therapists to keep the family from scapegoating the IP or using him or her as a way of avoiding problems in the rest of the system.

HOMEOSTASIS (BALANCE) Homeostasis means that the family system seeks to maintain its customary organization and functioning over time, and it tends to resist change. The family therapist can use the concept of homeostasis to explain why a certain family symptom has surfaced at a given time, why a specific member has become the IP, and what is likely to happen when the family begins to change.

THE EXTENDED FAMILY FIELD The extended family field includes the immediate family and the network of grandparents and other relatives of the family. This concept is used to explain the intergenerational transmission of attitudes, problems, behaviors, and other issues. Children and adolescents often benefit from family therapy that includes the extended family.

DIFFERENTIATION Differentiation refers to the ability of each family member to maintain his or her own sense of self, while remaining emotionally connected to the family. One mark of a healthy family is its capacity to allow members to differentiate, while family members still feel that they are members in good standing of the family.

TRIANGULAR RELATIONSHIPS Family systems theory maintains that emotional relationships in families are usually triangular. Whenever two members in the family system have problems with each other, they will "triangle in" a third member as a way of stabilizing their own relationship. The triangles in a family system usually interlock in a way that maintains family homeostasis. Common family triangles include a child and his or her parents; two children and one parent; a parent, a child, and a grandparent; three siblings; or, husband, wife, and an in-law.