Steven C. Hayes is an American clinical psychologist and professor of psychology at the University of Nevada, Reno. Born on August 12, 1948, he is best known for his work in developing Relational Frame Theory (RFT) and Acceptance and Commitment Therapy (ACT), which are part of a broader therapeutic approach known as contextual behavioral science. Hayes has authored numerous articles and books on these topics and has significantly influenced the field of behavior analysis and cognitive-behavioral therapy with his contributions to the understanding of human language, cognition, and the application of mindfulness and values-based interventions in psychotherapy. His work emphasizes psychological flexibility and the importance of accepting unpleasant thoughts and feelings while pursuing meaningful action aligned with personal values. Hayes has been a significant figure in the third wave of cognitive-behavioral therapies, which incorporate mindfulness and acceptance strategies.