This manual deals with the practical implementation of a routine data collection programme. The data collection 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 both through detailed discussion and by using simple examples. The examples are mostly based on situations in tropical fisheries, and in particular, experience has been drawn from develo ping 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 fishery 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 which assumes complete enumeration. The data collection methodology presented attempts to utilize whatever information can be obtained in practice in a developing country. Processing and storing of data (fisheries databases) and staff training are partly covered.