The field of drug utilization research has attracted increasing interest since its infancy in the 1960s. At a symposium in Oslo in 1969 entitled The Consumption of Drugs, it was agreed that an internationally accepted classification system for drug consumption studies was needed. At the same symposium the Drug UtilizationResearch Group (DURG) was established and tasked with the development of internationally applicable methods for drug utilization research.By modifying and extending the European Pharmaceutical Market Research Association (EPhMRA) classification system, Norwegian researchers developed a system known as the Anatomical TherapeuticChemical (ATC) classification. In order to measure drug use, it is important to have both a classification system and a unit of measurement. To deal with the objections against traditional units of measurement, a technical unit of measurement called the Defined Daily Dose (DDD) to be used in drug utilisation studies was developed. The purpose of the ATC/DDD system is to serve as a tool for drug utilization research in order to improve quality of drug use. One component of this is the presentation and comparison of drug consumption statistics at international and other levels. The classification of a substance in the ATC/DDD system is not a recommendation for use, nor does it imply any judgements about efficacy or relative efficacy of drugs and groups of drugs.The Anatomical Therapeutic Chemical classification system for veterinary medicinal products, ATCvet, has been developed by the Nordic Council on Medicines (NLN) in collaboration with the NLN’sATCvet working group, consisting of experts from the Nordic countries.The ATCvet system for the classification of veterinary medicines is based on the same overall principles as the ATC system for substances used in human medicine. In most cases an ATC code exists which can beused to classify a product in the ATCvet system. The ATCvet code is then created by placing the letter Q in front of the ATC code. In some cases, however, specific ATCvet codes are created, e.g. antibacterials for intramammary use (QJ51) and immunologicals (QI).