This report provides the JRC's scientific-technical evaluation of options to clarify the EC Recommendation on a definition of nanomaterial, published in 2011 (EC Recommendation 2011/696/EU). It is a follow-up report of two previous JRC publications, which compiled feedback on the experiences of stakeholders with the EC nanomaterial definition collected by JRC in 2013 and early 2014 (EUR 26567 EN, 2014), and provided an assessment of the collected information (EUR 26744 EN, 2014). The three JRC reports are part of the review process foreseen in the 2011 EC Recommendation. The evaluation shows that the scope of the definition regarding the origin of nanomaterials should remain unchanged, addressing natural, incidental as well as manufactured nanomaterials. Moreover, because of the regulatory purpose of the definition, there is little evidence to support deviating from size as the sole defining property of a nanoparticle or from the range of 1 nm to 100 nm as definition of the nanoscale. Besides the need for clarification of some terms used in the definition additional implementation guidance would be useful. The role of the volume specific surface area deserves clarification and a method to prove that a material is not a nanomaterial would be helpful. A strategy how to avoid unintended inclusion of materials and the list of explicitly included materials deserve also attention.