The Planning Group on Commercial Catch, Discards and Biological Sampling (PGCCDBS) 2012 was approached by the ICES Publications and Communications Group (PUBCOM) with the suggestion to combine the existing protocols on the age estimation of fish species within the ICES Area and publish them as an ICES Cooperative Research Report (CRR). This idea was received favourably by PGCCDBS. It was deemed important to (i) summarize the state of knowledge for key species, (ii) scrutinize, by peer review, the work done during the many calibration exercises, and, by doing so, (iii) promote an increase in quality. The aim of the present publication is to provide a comprehensive manual on the methodology of age estimation and validation and represents a collation of the state-of-the-art scientific work on the methods and validated age estimation of commercially exploited fish species across Europe. Having a collation of the latest methodologies by species grouping will also facilitate rapid and quality-assured development of methods suitable for new species.