Most therapy focuses on individuals, although psychotherapists also work with couples, families and groups.
"The main clinical precept of family systems theory is that individual problems must be understood within their larger family and environmental systems, which often provide the key to successful treatment. Family therapy provides a way of thinking in systemic, relational terms, and a set of strategies for intervening with individuals, couples, families, and other systems. Whether the client is a large family or a single person, family therapy focuses on changing relational interactions."
William J. Doherty and Susan H. McDaniel