Dr. Simpson's research on drug addiction and treatment effectiveness (reported in over 250 publications and 10 books or edited  volumes) includes several large-scale and longitudinal national evaluations.  Over the past 15 years, he has focused on assessments of client functioning and service delivery process, and how these factors influence treatment engagement and retention rates, stages of recovery, and long-term outcomes.  This work includes development of cognitive and behavioral interventions shown to enhance client services and improvements in program management.  His interests have expanded to the study of organizational behavior and its role in transferring evidence-based innovations into practice in community-based treatment agencies as well as criminal justice settings.  Simpson is an advisor to national and international research centers and government organizations that address drug abuse treatment and related policy issues, a Fellow in both American Psychological Association and American Psychological Society, and a member of the editorial boards for several journals.