These guidelines serve to provide a common understanding for operating the European Union Early Warning System on new psychoactive substances (Early Warning System) by detailing the rationale, steps, procedures, roles, and responsibilities. They reflect the requirements of Regulation (EC) No 1920/2006 (as amended) and Council Framework Decision 2004/757/JHA (as amended) with respect to information exchange and the Early Warning System, as well as those for the initial report, risk assessment, and control measures with respect to accepted scientific principles and required scientific evidence.