Family health is dependent upon the individual family members' capacity to establish mature relationships with one another. The development of these relationships occurs through the experiential ranging of family members between the poles of symbiotic union and individuation, a continual process of ego development through self‐other differentiation. A model which encompasses the family system's tolerance for ranging is presented in this paper. The model aids the clinician in making a family developmental diagnosis and in understanding family treatment as a growth experienc