Introduction to the special series on motivational interviewing and psychotherapy.

Clinical and research applications of motivational interviewing (MI) have grown at a remarkable pace over the past 25 years. Most of this work has targeted the addictions and health-related behaviors. The series of articles in this issue highlight a rapidly accelerating recent trend: the application of MI to other problems typically seen in clinical practice. This introductory article describes MI, its core principles, treatment methods, and the variety of ways in which it has been employed. The 6 case reports in this issue are then described. They illustrate how MI can be employed with generalized anxiety, adolescent depression, lifestyle changes, social anxiety disorder, suicidality, and intimate partner violence. The series of articles in this issue concludes with a commentary on the cases and a practice-friendly review of outcome research on MI.