Mark Tarrant is Professor of Psychology at the University of Plymouth, UK. His work focuses on the development and evaluation of group-based behaviour change interventions for supporting health. He has published more than 70 articles and book chapters, including in leading international journals (e.g., Psychological Science, Health Psychology Review), and has been funded by major research councils (e.g., NIHR, MRC, ESRC) and charities (e.g., Stroke Association). Martin S. Hagger is Distinguished Professor at the University of California, Merced, Professor (Behaviour Change) in the Faculty of Sport and Health Sciences, University of Jyväskylä, Finland, and Adjunct Professor and Research Consultant in the School of Applied Psychology, Griffith University. His research applies social cognition and motivational theory to predict, understand, and change health behaviours. He has published over 400 articles, chapters, and books, and served as editor of major scholarly peer-reviewed journals.