This review covers the literature published in 2001 for marine natural products, with 495 citations (365 for the period January to December 2001) referring to 793 compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (680 for 2001), together with their relevant biological activities, source organisms and country of origin. Syntheses that confirm or revise structures orstereochemistries have been included (113), including any first total syntheses of a marine natural product.