Robert D. Zettle is Professor of Psychology at Wichita State University, USA. He serves on the editorial board of several journals including Behavior Modification, International Journal of Behavioral Consultation & Therapy and The Psychological Record. Professor Zettle has contributed many chapters to various books, and is the author of ACT for Depression (2007). Steven C. Hayes is Nevada Foundation Professor at the Department of Psychology at the University of Nevada, USA. An author of 36 books including the best selling Get Out of Your Mind and Into Your Life (2005), his research demonstrates how language and thought leads to human suffering. He developed Acceptance and Commitment Therapy, and Relational Frame Theory, a contextual approach to language and cognition. Dr. Hayes has received the Lifetime Achievement Award from the Association for Behavioral and Cognitive Therapy. Dermot Barnes-Holmes is foundation Professor of Psychology at the National University of Ireland Maynooth, and is known for the analysis of human language and cognition through the development of Relational Frame Theory with Steven C. Hayes, and its application in various psychological settings. Professor Barnes-Holmes has published over 250 scientific articles, chapters and books. Tony Biglan is Professor of Psychology andDirector at the Center for Prevention of Problems in Early Adolescence at Oregon Research Institute, USA. His research over the past 30 years has helped to identify effective family, school, and community interventions to prevent the most common and costly problems of childhood and adolescence.