The European Commission’s (EC’s) Scientific Committee on Emerging and Newly Identified Health Risks has approved a definition for “nanomaterial” as a basis for future regulatory safety evaluations and risk assessments. The committee concluded that size is the most relevant consideration in defining the term, and that no scientific justification exists to prefer any specific size limit other than the range from 1 to 100 nanometers. According to the committee, “size influences bio-distribution (and distribution kinetics) in an organism or in an ecosystem which should be taken into consideration in the risk assessment of nanomaterials.” The committee decided not to distinguish between natural and manufactured nanomaterials in its definition.