The Organization for Economic Cooperation and Development (OECD) recently published a new document in its series on the safety of manufactured nanomaterials, Important Issues on Risk Assessment of Manufactured Nanomaterials. The document was prepared by Steering Group Six of the Working Party on Manufactured Nanomaterials (WPMN), which is leading the project on cooperation on risk assessment, and was endorsed at the ninth meeting of the WPMN in December 2011. The document provides the current practices, challenges, and strategies for assessing risk in circumstances where data are limited, and there is a necessity for more research on specific risk assessment issues. OECD cautions that it is not to be construed to imply scientific and/or policy endorsement of any specific risk assessment methods or models, however. OECD notes that “this document is a living document,” and was current at the time of WPMN’s ninth meeting in December 2011. The document is subject to amendment and refinement as research affords further understanding of how to assess and manage nanomaterials.