Kevin L. Polk, PhD, is a clinical psychologist who has been a practicing for twenty-six years, primarily helping veterans and others with troubling trauma memories. For the past eleven years, he has dedicated himself to the study of acceptance and commitment therapy (ACT)—spending close to 27,000 hours studying the philosophy and theory behind ACT, and learning and designing ACT interventions. He is a peer-reviewed ACT trainer who is passionate about teaching others how to use the ACT Matrix to increase& psychological flexibility and valued living. Find out more at www.drkevinpolk.com.

Benjamin Schoendorff, MA, MSc, is director of the Contextual Psychology Institute in Montreal, QC, Canada. He is involved in ACT research at the Montreal University Mental Health Institute, and a clinical psychologist in private practice working with adults, children, teens, and couples. Schoendorff is passionate about making ACT simple for both therapists and clients. He’s authored and coauthored several ACT books in French, coedited The ACT Matrix with Kevin Polk, and coauthored The ACT Practitioner’s Guide to the Science of Compassion with Dennis Tirch and Laura Silberstein. A peer-reviewed ACT trainer and certified functional analytic psychotherapy (FAP) trainer, Schoendorff has led approximately two-hundred workshops around the world, and is currently disseminating the six-step ACT Matrix approach at the heart of this book. His workshops are widely appreciated for their direct clinical applicability, deep humanity, and warm sense of humor. In his spare time, Schoendorff loves travelling with his wife and young son Thomas, and sharing his love for ACT and the Matrix. Find out more at www.contextpsy.com.

Mark Webster is a registered psychotherapist with the United Kingdom Council for Psychotherapy (UKCP). Following a first career in the computer industry, he worked for ten years at a specialist personality disorder clinic in the National Health Service (NHS). His involvement in third-wave cognitive behavioral therapy (CBT) began with dialectical behavior therapy (DBT) in 1997, which led to an early interest in ACT. Webster has been an ACT trainer since 2002, and currently runs his own business specializing in acceptance and mindfulness therapies. In 2005, he founded the ACT special interest group within the British Association for Behavioural and Cognitive Psychotherapies (BABCP). In 2008, with Kevin Polk, he created the ACT Matrix, a very user-friendly way of delivering ACT in a group setting. Webster’s main interest is in finding ways to make ACT more widely available outside of traditional mental health settings. He has recently founded a community interest company called ACT Peer Recovery CIC to develop peer recovery in addiction and mental health. In addition to offering training in mental health, he regularly conducts ACT workshops for physical health practitioners, including nurses, physiotherapists, and occupational therapists. Webster has been practicing mindfulness for over twenty-five years, and is current chair of the UKCP’s Cognitive Psychotherapies College.

Fabian O. Olaz, PsyD, is adjunct professor in clinical psychology and psychotherapies, and researcher and director of the Interpersonal Behavior Laboratory in the faculty of psychology at the National University of Córdoba in Argentina. He is an ACT and functional analytic psychotherapy supervisor and psychotherapist at the Integral Center of Contextual Psychotherapy (CIPCO), and a recognized trainer in Argentina, Brazil, and other South American countries.