Sea cucumbers (Holothurians) are a group of marine invertebrates that are harvested worldwide in tropical and subtropical countries. Over the past decades, a significant increase in the demand for sea cucumber has led to an explosion in exploitation often resulting in population declines in many producing nations. Because of the importance of sea cucumbers as a source of livelihood for many artisanal fishers from developing countries and as a globally traded product, much interest has been generated for information on their biology, ecology and fisheries management. Although management agencies and fishing communities have recognized that sea cucumber fisheries are in trouble worldwide, attempts at management have been largely unsuccessful due to several factors including: 1) the vulnerability of sea cucumbers to harvesting, 2) the artisanal nature of the fishery that prevents fisher communities from using alternative coping mechanisms and 3) the institutional and socio-economic barriers to management. Sea cucumber production has been declining in nations of the Western Indian Ocean in the last ten years. The reasons for the decline include: 1) a lack of ecological information for understanding species life histories, 2) a lack of understanding of the socio-economic realities of the fishery and 3) inadequate monitoring and enforcement of fishery regulations. The Western Indian Ocean Marine Science Association (WIOMSA) as part of its aim to serve the information needs of resource managers and communities for the sustainable management of marine resources in the WIO, approved a ‘Regional Sea Cucumber Project’ in 2006. This review was prepared as the baseline study of the project and aims to provide a comprehensive synthesis of the current state of knowledge on sea cucumbers in the WIO. The information used in the review comes from many sources including journal articles, theses and dissertations, and reports on all aspects of sea cucumbers in the region. Although the report focuses on the five countries (Kenya, La Reunion, Madagascar, Seychelles, Tanzania) that are involved in the project, a brief description of the status of sea cucumbers in other countries of the WIO is also included.