In response to research findings of insufficient family involvement in mental health services for people with severe mental illness, this grounded theory study examines case managers' interactions with families of clients in Assertive Community Treatment (ACT). Findings suggest that case managers conceptualize families as sources of social connections, rather than sources of care, for clients. This conceptualization is influenced by case managers' goals, which also guide their assessments of families for involvement in treatment in terms of the extent to which families help attain treatment goals. In developing strategies to work with families, case managers engage in ongoing assessments and consider client permission for family involvement in treatment, family availability to clients, and family wishes for involvement in treatment. Three case examples illustrate the relationships among case managers' goals, assessments of families, and selections of work strategies. The potential role of the ACT model in shaping this particular view on families is also discussed.