Theorists such as Farber argue that in adolescence passionate love first appears in all its intensity. Both adolescence and passion are "intense, overwhelming, passionate, consuming, exciting, and confusing". As yet, however, clinicians have been given little guidance as to how to deal with adolescents caught up in their passionate feelings. Nor has there been much research into the nature of passionate love. In Section I of this paper, we define passionate love, explain the necessity of developing a scale to measure this concept, and review evidence as to the nature of passionate love. In Section 2, we report a series of studies conducted in developing the Passionate Love Scale (the PLS). We present evidence as to the PLS's reliability, validity, and relationship to other factors involved in close relationships. We end by describing how we have used this scale in family therapy to open conversations about the nature of passionate love/companionate love/and intimacy... and discussing profitable directions for subsequent research.