This article deals with the implementation of ecosystem-based marine management in the Baltic Sea. It explores and documents in particular the preliminary lessons from environmental and fisheries management with reference to the Helsinki Commission Group for implementation of the ecosystem
approach and the Baltic Sea Fisheries Forum, both examples of regionalisation processes in order to
implement ecosystem-based marine management. The Helsinki Commission Group for mplementation of the ecosystem approach is a joint management body for the implementation of the Baltic Sea Action Plan and the European Union's Marine Strategy Framework Directive. The Baltic Sea Fisheries Forum is a new governing body to facilitate regional cooperation in fisheries management. The aim of the article is twofold: a) to describe and discuss two different pathways of regionalisation in the Baltic Sea and b) to explore how these forms of regionalisation could contribute to the implementation of governance structures needed to implement ecosystem-based marine management at the level of a regional sea - efficiently, legitimately and effectively. We conclude that a nested governance structure could be developed by building upon existing institutions while learning from new initiatives to organise stakeholder involvement.