JoAnne Dahl, PhD, is professor of psychology at Uppsala University, Sweden. JoAnne is a clinical psychologist specializing in behavior medicine. She is coauthor of the The Art and Science of Valuing in Psychotherapy, Acceptance and Commitment Therapy for Chronic Pain, Living Beyond Your Pain, and ACT and RFT in Relationships. Steven C. Hayes, PhD, is Nevada Foundation Professor in the department of psychology at the University of Nevada, Reno. He has been president of numerous professional organizations, is author of forty-five books and nearly 650 scientific articles, and is among the most cited living psychologists. He has shown in his research how language and thought leads to human suffering, and is originator and codeveloper of acceptance and commitment therapy (ACT): a powerful therapy method that is useful in a wide variety of areas; relational frame theory (RFT): an empirical program in language and cognition; and process-based therapy (with Stefan G. Hofmann). Tobias Lundgren, MS, is a licensed clinical psychologist specializing in cognitive behavior therapy and ACT. He is an active clinician and a researcher in the areas of behavior medicine, psychometrics, and self-destructive behavior. Lundgren is affiliated with the psychology department at the University of Uppsala in Sweden, and has conducted research in many developing countries.