Identifying, resolving and preventing DRPs are considered cornerstones in pharmaceutical care. The Pharmaceutical Care Network Europe (PCNE) defines a DRP as “An event or circumstance involving drug therapy that actually or potentially interferes with desired health outcomes ”. Another term sometimes mixed up with DRPs is “medication error”, defined by the European Medicines Agency (EMA) as “an unintended failure in the drug treatment process that leads to, or has the potential to lead to, harm to the patient ”. The natural dividing line between a DRP and a medication error would then be whether the deviation has been committed by a patient or a health professional, respectively, although there is no full consensus on the interpretation of the two terms. Classifying DRPs is desirable for the development of pharmaceutical care practice and research and facilitates documentation and follow-up, important cornerstones of pharmaceutical care. Many different DRP classification systems have been created throughout the years with both similarities and differences. It is of great importance that a DRP classification system is easy to use in daily pharmacy practice, that it is accepted, feasible and validated. The DRP identification rate varies a lot among studies and practices, from less than one DRP per patient to several, depending on a number of factors. Several ways to increase the rate have been tried in different countries.