Predicted no effect concentrations (PNECs) or Environmental Quality Standards (EQSs), are derived in a large number of legal frameworks worldwide. When deriving these safe concentrations, it is necessary to evaluate the reliability and relevance of ecotoxicity studies. This evaluation is often subject to expert judgment, which may introduce bias and decrease consistency when risk assessors evaluate the same study. The CRED-project, short for Criteria for Reporting and Evaluating ecotoxicity Data, attempts to address this problem. It aims at improving reproducibility, transparency and consistency of reliability and relevance evaluations of aquatic ecotoxicity studies amongst regulatory frameworks, countries, institutes and individual assessors. In this paper the CRED evaluation method is presented. It includes a set of 20 reliability and 13 relevance criteria, accompanied by extensive guidance. Risk assessors who participated in the CRED ring test evaluated the CRED evaluation method to be more accurate, applicable, consistent and transparent than the often-used Klimisch method. The CRED evaluation method is accompanied by reporting recommendations for aquatic ecotoxicity studies, with 50 specific criteria divided into six categories: general information, test design, test substance, test organism, exposure conditions, and statistical design and biological response. An ecotoxicity study in which all important information is reported is more likely to be considered for regulatory use, and proper reporting may also help in the peer-review process.