This chapter was written during the Workshop on Age Validation of Gadoids (WKAVGS 2013) which was held 6–10 May 2013 at Imedea in Esporles, Mallorca. The terms of reference for the workshop were to: 1. Review information on age estimations, otolith exchanges, workshops, and validation works done so far on the following species: European hake, cod, pollock, saithe, haddock, whiting, and blue whiting; 2. Assemble and compare the results of different validation methods (i.e. marking and recapture, marking the calcified structure, marginal increment analysis, marginal analysis, modal progression analysis, length back-calculation, etc.); 3. Discuss and propose the most appropriate validation methods of age and growth pattern of calcified structures (CS), for each species and stock; 4. Propose the appropriate validation methods to recognize the growth check as well as the spawning ring, demersal ring, migration ring, etc.; 5. Propose an ICES Cooperative Research Report on: Age Validation Studies for ICES and GCFM Gadoid Stocks to ICES PGCCDBS, using previous studies and the outcome of this workshop; 6. Based on results, conclusions, and recommendations from this workshop to initiate and design an international cooperation project on validation methods (such as on the validation of checks and spawning rings) to commence after the workshop.