Best known for his pioneering introduction of the Addiction Severity Index and Treatment Services Review in the 1980s, McLellan later conceptualized data-driven measurement of treatment effectiveness, performance-based monitoring, and analysis of the nation’s substance abuse treatment system as an “industry” beset with the same organizational, staffing and funding problems overcome in other problem-plagued industries. Through his research and extensive knowledge of substance abuse treatment systems, McLellan has become a persuasive proponent of the view that addiction is a chronically relapsing condition, one that must be continually monitored and managed. McLellan has published more than 400 articles and chapters on addiction research and serves as Editor in Chief of the Journal of Substance Abuse Treatment. He serves on the editorial boards and as a reviewer of numerous medical and scientific journals, and is advisor to numerous government and nonprofit scientific organizations, including the Office of National Drug Control Policy, Research and Evaluation; the National Practice Laboratory of the American Psychiatric Association, the Swiss National Science Foundation, the World Health Organization, and the Greek government.