To effectively manage our fisheries, we need to manage fish in the context of the environment in which they exist, that is an ecosystem. This means understanding the complex ecological and socioeconomic environments in which fish and fisheries exist. It also means anticipating the effects that fishery management will have on the ecosystem and the effects that ecosystem will have on fisheries. Practical application of a comprehensive ecosystem-based fisheries management approach is still in its early stage of development by the regional organizations concerned with fisheries and the marine and coastal environment. It is time that these organizations grasp its potential for cooperation. This awareness must be expanded and actions taken to implement this approach. This paper was presented at the 3rd Global Meeting of the Regional Seas Conventions (RSCs), organized by UNEP in Monaco 6-9 November 2000 and at the 2nd Meeting of Regional Fisheries Management Organizations, at FAO Headquarters, in February 2001. The publication has also benefited from the inputs of the participants to these meetings. The purpose of this publication is to present considerations which can serve as the basis for potential cooperation between RFBs and RSCs. It describes the concept of ecosystem-based fisheries management, the relevant mandates and activities of RFBs and RFCs and the relationship and mutual relevance of their work. Possible mechanisms for cooperation, and issues for future consideration, are identified. It is anticipated that such cooperation could best be implemented on a site-specific or regional basis, after initial consideration at the global level by RFBs and RSCs. UNEP will embark during the following years in a process of collaboration with FAO to explore the opportunities and challenges for coordinated activities on ecosystem-based management of fisheries.