The term high conflict is used regularly across various literatures; such as divorce, family court, and psychotherapy; to describe relationships that are mired in conflict. Despite its widespread use, the term has not been precisely defined in a clinically meaningful way. This article offers a definition of high conflict based on a synthesis of previous literatures related to high conflict, observations of court personnel, and the authors' own clinical experiences working with this population. A case study illustrates the pervasive negative exchanges and hostile insecure emotional environment that characterize these couples. The implications of this definition for clinical practice are also discussed.