1 Marie Jauffret-Roustide is with the Centre d'Étude des Mouvements Sociaux (Inserm U1276/CNRS UMR 8044/EHESS), Paris, France. Esben Houborg and Vibeke Asmussen Frank are with the Center for Alcohol and Drug Research, Aarhus University, Copenhagen, Denmark. Matthew Southwell is with the European Network of People Who Use Drugs, Bath, UK. Daphné Chronopoulou is with the European Network of People Who Use Drugs, Mykonos, Greece. Jean-Maxence Granier is with Auto-Support des Usagers de Drogues/Self-Support for People Who Use Drugs, Paris, France. Alex Stevens is with the School of Social Policy, Sociology and Social Research, University of Kent, Canterbury, UK. Tim Rhodes is with the London School of Hygiene and Tropical Medicine, London, UK. Marie Jauffret-Roustide is also a Guest Editor of this supplement issue.