This manual starts with an introduction to the mathematical models applied in fish stock assessment. The basic assumptions about a model and the concepts of variation rates of a characteristic in relation to time are presented. The concept of cohort and models for the individual growth of the cohort are developed. In the chapter concerning the study of the stock, the fishing pattern and its components are defined, the most used models for the stock-recruitment relation are presented, as well as the short- and long-term projections of a stock. With regard to fisheries resources management, the discussion is focused on the biological reference points. Finally, the general methods of estimating parameters with special relevance to the cohort analysis by age and length are described. The exercises from the last course held in the Instituto de Investigacao das Pescas e do Mar, Portugal are presented by the author and the scientist Manuela Azevedo.