The European Commission (EC) Joint Research Center (JRC) recently published a report entitled NANoREG harmonised terminology for environmental health and safety assessment of nanomaterials, developed within the NANoREG project: “A common European approach to the regulatory testing of nanomaterials.” The report states that it represents the project’s attempt at bringing common understanding and consistency in the use of key terms in the environmental health and safety (EHS) assessment of nanomaterials. The objective of the report is to publish the harmonized terminology that has been developed and used within NANoREG. According to the report, all project partners have agreed upon and adopted the terminology in their activities and related documents. The report specifically includes: (1) the methodology used to select key terms that form the harmonized terminology and to develop harmonized definitions; (2) the existing literature definitions that have been used as a starting point to develop for each key term a harmonized definition; and (3) the reason(s) behind the choices that have been made in drafting a definition. The discussion on the key terms to be considered for the harmonized terminology led to the selection of 43 key terms. The list includes terms with international regulatory relevance, such as those defined at the Organization of Economic Cooperation and Development (OECD) level, as well as terms that have a specific meaning and use under the Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) regulation. According to the report, it has “already proven very useful” in the context of OECD work, as a support document to the April 13-14, 2016, OECD Expert Meeting on “Grouping and read-across for the hazard assessment of manufactured nanomaterials,” and in a regulatory context, as a support document to the work recently released by the National Institute for Public Health and the Environment (RIVM), European Chemicals Agency (ECHA), and JRC on using (eco)toxicological data for bridging data gaps between nanoforms of the same substance.