Over the past few years the analysis of drug residues in sewage has been promoted as a means of estimating the level of drug use in communities. Measured drug residue concentrations in the sewage are used to determine the load (total mass) of the drug being used by the entire community. Knowledge of the size or population of the community then allows for the calculation of drug-use relative to population (typically drug-mass/day/1000 inhabitants) which facilitates comparisons between differing communities or populations. Studies have been performed in many European countries, including Norway, as well as in the US and Australia. The approach has successfully estimated the use of cocaine, amphetamine, methampheta-mine, MDMA, cannabis, nicotine and alcohol. The analysis of biomarkers of drug use in sewage has great potential to support and complement existing techniques for estimating levels of drug use, and as such has been identified as a promising development by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA; www.emcdda.europa.eu/wastewater-analysis). The approach is not without its challenges, and ongoing collaboration across Europe aims at agreeing upon best-practice and harmonising the methods being used. In Norway development is being performed through the NFR RUSMIDDEL funded DrugMon ( www.niva.no/drugmon) project that has led to the development of many new techniques, significantly improved our understanding of the uncertainties associated with the approach and allowed the coordination of Europe wide collaboration which has included all important intercalibration exercises. Application of the technique can provide evidence-based and real-time estimates of collective drug use with the resulting data used to improve the much needed estimates of drug use and dependency.