Covering: 2013. Previous review: Nat. Prod. Rep. , 2014, 31 , 160-258 This review covers the literature published in 2013 for marine natural products (MNPs), with 982 citations (644 for the period January to December 2013) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1163 for 2013), together with the relevant biological activities, source organisms and country of origin. Reviews, biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included. This review of marine natural products for 2013 describes 1137 new compounds and reports structural revisions and assignments of absolute configurations for previously described compounds. Included is a report of the anticancer sponge metabolite PM060184 that has undergone a remarkably rapid development from discovery in 2005 to the commencement of phase I clinical trials in 2011.