Data are quality assured using internal and external programmes. For example, the national laboratories that take part in monitoring programmes related to contaminants and biological effects that submit information to ICES, subscribe to the Quality Assurance of Information for Marine Environmental Monitoring in Europe (QUASIMEME) or the Biological Effects Quality Assurance in Monitoring Programmes (BEQUALM) inter-laboratory proficiency-testing schemes and perform internal quality assurance. ICES operates through a network of scientific expert and advisory groups. These groups, and the processes they feed into, act as a quality check on the marine evidence, both in terms of how the evidence was gathered and how the evidence has been subsequently treated. The groups, in cooperation with regional programmes under the Regional Sea Conventions, set standards and guidelines for the collection, transmission and analysis of these data. In addition, the ICES Secretariat provides supplementary quality assurance through its internal programmes related to the different types of marine data collection datasets, which is fedback to the participating national and regional programmes. These internal and external programmes and procedures have been established over a period of 30 or more years. They continue to evolve and strive to reflect the best available practices in the collection and treatment of marine data relevant to the ICES community.