New or Novel Psychoactive Substances (NPS) imitate the effects of illegal drugs and are commonly (although misleadingly) referred to as „legal highs‟. Over the last decade the use of NPS has expanded in Scotland. Current data sources and anecdotal reports have identified a number of vulnerable or potentially at risk groups. This report presents results of mixed methods research on NPS use among five key target populations: vulnerable young people, people in contact with mental health services, people affected by homelessness, people who inject drugs (PWID) and men who have sex with men (MSM).