As a distinguished scholar over the past 45 years, Michel Hersen has left an indelible mark on the field of behavior therapy and clinical psychology. One of his most enduring legacies is his early research work in the area of social skills assessment and training, with special attention to assertiveness training. His basic analogue and clinical outcome studies have served as essential building blocks for current evidence-based treatments. His long and distinguished career has significantly impacted the lives of colleagues, students, and patients alike.