This manual deals with the practical implementation of a routine data collection programme. This programme is developed through a top-down approach, from the identification of the objectives down to the practical recording and management of data obtained from the fishery. The issues are dealt with through both detailed discussion and by using simple examples. These examples are mostly based on situations in tropical fisheries and, in particular, experience has been drawn from developing a data collection programme in Viet Nam. The main questions addressed in the manual are which fisheries data to collect, where and when to collect them. Only data collected from commercial marine capture fisheries are considered (data from freshwater fisheries, cultured fish and experimental fisheries are excluded). The methodologies used are mainly appropriate for a tropical developing country with many small (artisanal) vessels and a few large (industrial) vessels. The methodology is the "sample-based approach" - the manual does not deal with a methodology that assumes complete enumeration. The data collection methodology presented attempts to utilize whatever information can be obtained in practice in a developing country.