This is a framework for reliability and relevance evaluation of ecotoxicity data for nanomaterials. The nanoCRED evaluation criteria, and accompanying guidance, were developed to be used in combination with those developed through the ‘Criteria for Reporting and Evaluating Ecotoxicity Data (CRED)’ project. This approach can accommodate all types of nanomaterials, all types of aquatic ecotoxicity studies, and qualitative as well as quantitative data evaluation requirements. Furthermore, it is practically feasible to implement and directly applicable in European as well as international regulatory frameworks.