The starting point for this paper is that family therapy lacks a theoretical frame of reference of its own; thus a stepwise search for such a frame of reference is described. First, social systems are defined as communication systems. Second, it is shown in what way a family can be seen as a social system. With the help of the theory of social systems of the sociologist Luhmann, a theoretical frame of reference for systems therapy is drafted. Finally, we hint at the implications such a theoretical framework could have for clinical practice.