The marine data manual is published by the UN Environment World Conservation Monitoring Centre (UNEP-WCMC) as a supplement to the Ocean Data Viewer (data.unep-wcmc.org). The availability and appropriate use of marine and coastal data form the foundation of effective decision-making. This manual, as the second edition of the manual published by Martin et al. in 2014, aims to provide an overview of global marine and coastal datasets of biodiversity importance. The intention is to address the fragmented information and guidance for users of marine data. Although not exhaustive, this review has resulted in the identification of 128 datasets, databases and data portals (Annex 2). The report also includes detailed standardised metadata for 69 of these reviewed datasets (Annex 3). The various challenges, gaps and limitations which can be presented by coastal and marine data are also discussed. If you have any comments, suggestions, or queries, please contact: firstname.lastname@example.org.