Public participation is one of the central principles of Integrated Coastal Zone Management (ICZM). However, within current public participation practice in coastal decision making there remain questions regarding whether or not the project leaders or participation processes can be considered legitimate. The paper explores the issue of legitimacy, examining case studies of coastal decision making processes from Belgium and France, focusing on the legal constraints for public participation including degree of formality and government style. It reveals that there are legitimacy issues in public participation related to the legal and institutional framework of the project, as well as to the knowledge base, and characteristics of the stakeholders and their interests. This study concludes that legitimacy issues in an ICZM process cannot be solved entirely through an institutional framework and associated legislation. (C) 2010 Elsevier Ltd. All rights reserved.