This Fisheries Technical Paper provides guidance for the measurement and assessment of fishing capacity, with the aim of facilitating the implementation of the International Plan of Action for the Management of Fishing Capacity. It provides a discussion and overview of the various concepts of capacity and capacity utilization and potential methods for estimating capacity discussed at the FAO Technical Consultation on the Measurement of Fishing Capacity held in Mexico City from 29 November to 3 December 1999. The paper also introduces some more recent methodologies for examining capacity in fisheries. Its specific objective is to provide the information necessary for developing a widely accepted definition of capacity for fisheries as well as sufficient detail about various methods for estimating capacity to permit an empirical assessment of fishing capacity conditional on the types of data typically available for fisheries. The document initially discusses concepts and issues necessary for understanding capacity and capacity utilization in fisheries, followed by the primary methods often used to estimate capacity. It also gives empirical examples of how the various approaches can be used to estimate and assess capacity. Finally, a potential framework for assessing overcapacity is presented and discussed.