This report looks at the use of new psychoactive substances (NPS) in prison settings. This is a rapidly developing phenomenon, but empirical data are currently scarce and patchy. There is growing evidence that NPS are responsible for a large share of drug-related problems in some European prisons and appropriate responses are mostly lacking. This preliminary analysis is the outcome of a targeted rapid information assessment or ‘trendspotter’ study carried out by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) between August and December 2017. Trendspotter studies are based on a multi-method approach and expert opinion. They are intended to elaborate emerging issues and prompt discussion and, if required, more formal follow-up.