A two-page summary of the information on nanotechnology and manufactured nanomaterials contained in the 2020 UNEP Assessment Report on Issues of Concern: Chemicals and Waste Issues Posing Risks to Human Health and the Environment and the 2019 Global Chemicals Outlook II. While no definition has been internationally agreed upon, nanomaterials are commonly defined as materials having at least one external or internal dimension between 1 and 100 nanometers.