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).
Michael P. Twohig, PhD, is well known for his work in ACT and OCD, which is closely related to perfectionism. Twohig is professor in the psychology department at Utah State University. He is past president of the ACBS, and a current member of the Association for Behavioral and Cognitive Therapies (ABCT). He has written more than 170 peer-reviewed publications, seven books, and has received funding from many organizations, including the National Institute of Mental Health (NIMH).