This publication provides an overview of the latest information available on the use of new psychoactive substances (NPS) and related problems in European prisons based on a rapid information assessment carried out by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA). The study complements data from a range of established sources. The EMCDDA has been routinely collecting data on illicit drug use among prisoners for over 15 years through a combination of qualitative and quantitative monitoring tools, although the primary focus has been on controlled substances. The EMCDDA also collects information on NPS and, in 2017, was monitoring a total of over 670 NPS that have been notified to the EU Early Warning System (EWS). The use of NPS by high-risk drug users has recently been explored by the EMCDDA (2017a). The study found that while consumption levels of these drugs were low overall in Europe, the smoking of synthetic cannabinoids among some marginalised populations, including prisoners, appeared to be an emerging but poorly understood problem in many European countries. This study was prompted therefore by the conclusion that NPS use among prisoners appears to be a rapidly developing phenomenon and there is growing concern in some countries that NPS may be responsible for a large share of drug-related problems in prison, while appropriate responses are mostly lacking. However, empirical data are currently scarce and patchy, as monitoring drug use among prisoners in general, and NPS use in particular, at the European level is challenging due to the different study designs applied and limited systematic data collection. To investigate the extent, nature and impact of these developments the EMCDDA carried out a targeted rapid information assessment between August and December 2017. The aim of the study was to map and increase understanding of NPS use in prisons in Europe, including prevalence and patterns of use, the underlying contributing factors, associated harms and market and supply features of NPS use in prisons, as well as the responses implemented to address NPS-related problems in prison settings.