NIDA International Program Director Steven W. Gust, Ph.D., co-chaired the Third International Symposium on Drug-Impaired Driving, which was held in Lisbon, Portugal, on October 23, 2017. The prevalence of drug-impaired driving has begun to rival that of alcohol-impaired driving in some parts of the world, resulting in a greater focus on the ability to detect drug-impaired drivers using roadside screening tools and efforts to establish “per se” limits for drug use. The session brought together key stakeholders who have advanced the field to share the latest developments in drug screening, testing, and detection; review regulatory models; present new research; and identify knowledge gaps. Dr. Gust also chaired a session on the implications of cannabis policy changes on impaired driving. U.S. speakers at the symposium included Richard Compton, National Highway Traffic Safety Administration; Darrin Grondel, Washington State Traffic Safety Commission and secretary of the Governors Highway Safety Commission; and Glenn Davis, Colorado Department of Transportation. The symposium was a collaborative effort between the Canadian Centre on Substance Use and Addiction (CCSA), the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), the New Zealand Drug Foundation, and the NIDA International Program. It was held immediately prior to the Second European Conference on Addictive Behaviours and Dependencies.