Tuna and billfish are highly migratory species, with their habitat and migratory pathways often crossing the Exclusive Economic Zone of different countries. The extent of population structure, habitats and behavior of these fishes are emerging management and conservation issues requiring the attention of fisheries scientists. Tagging programs are widely recognized as important tools for understanding the population dynamics, dispersal patterns and fisheries interactions of fish populations. The objective of this project is to conduct tagging of main commercial species of billfishes, sailfish (Istiophorus platypterus),black marlin (Istiompax indica), striped marlin (Kajikia audax), blue marlin (Makaira nigricans) and tunas, yellowfin tuna (Thunnus albacores)and longtail tuna (Thunnus tonggol) in waters off Taiwan. These results can increase understanding of the population dynamics of billfish and tuna in eastern Taiwan. These will be the important input parameters for the stock assessment and scientific references on setting management strategies.