Mark Williams, PhD, is Professor of Clinical Psychology and Wellcome Principal Research Fellow at Oxford University. John Teasdale, PhD, has held senior research appointments in the Department of Psychiatry, University of Oxford, and the Cognition and Brain Sciences Unit, Cambridge, UK. He has received a Distinguished Scientist Award from the American Psychological Association, and is a Fellow of both the British Academy and the Academy of Medical Sciences. Zindel Segal, PhD, is the Morgan Firestone Chair in Psychotherapy at the University of Toronto and Director of the Cognitive Behaviour Therapy Unit at the Centre for Addiction and Mental Health. Jon Kabat-Zinn, PhD, is internationally known for his work as a scientist, writer, and teacher. He is Professor Emeritus of Medicine at the University of Massachusetts Medical School, where he was founding executive director of the Center for Mindfulness in Medicine, Health Care, and Society.