At least 1.1 million Europeans are estimated to have received treatment for drug dependence during 2009, mostly through opioid substitution, detoxification and psychosocial interventions, delivered in a variety of settings. While more than half of the clients received opioid substitution treatment, a substantial number received other forms of treatment for problems related to opioids, stimulants, cannabis and other illicit drugs. The quality of interventions is underpinned by treatment guidelines. This Selected issue focuses on the topic of improving treatment quality by the development of guidelines, and provides an overview of existing national guidelines for the treatment of drug dependence in Europe.