This chapter discusses how family is considered a specialized type of group and describes the use of a genogram in family assessment. It provides an overview of general systems theory and exposes the reader to systems thinking. The chapter discusses groups, group therapy, and family therapy as they relate to systems theory and systems thinking with examples of applications to each. It reviews examples of how systems theory is reflected in nursing theory. Professional or more formal group affiliations may include the clinical group of students in the psychiatric-mental health nursing rotation, the student body of a college of nursing, all student nurses belonging to Student Nurses Association, club memberships, as well as work-related groups such as the treatment team in the place of employment. The chapter integrates exercises to facilitate understanding of personal experiences within systems thinking and its relevance to psychiatric-mental health nursing practice.