This book analyses the question whether states whose nationals are beneficial owners or operators of vessels engaged in illegal fishing (vessel owner states) in a foreign Exclusive Economic Zone (EEZ) have an obligation to act against such nationals with a focus on the situation in West Africa, one of the worst affected regions. It reviews the international legal regime that applies to fisheries in an EEZ and considers various sources of international law as well as state practice, including the rules of the European Union and the USA, that support the argument that there is such an obli-gation. Suggestions are given as to how vessel owner, coastal and flag states can give effect to this obligation.