This chapter addresses systems theory as applied to families and their interaction patterns. Since the 1930s, general systems theory (GST) has influenced a wide range of disciplines, such as medical and health sciences, agriculture, computer and information studies, and the social sciences. Scholars from many applied fields that address family functioning (including psychology, family therapy, and sociology) use and adapt GST to understand interaction patterns within human systems. Systems theory recognizes that all systems, including families, are characterized by several important characteristics: interdependence, wholeness, self-regulating patterns, openness, feedback, hierarchy/complex subgroups, interactive complexity and equifinality. The chapter considers how attuning themselves to systems theory concepts may be useful in their own relational lives. Systems theory encourages a focus on what is created through overall patterns; causality and/or individual responsibility are not often pinpointed. However, there is some concern that the focus on overall patterns may not do enough to destabilize unhealthy or dangerous systems.