The present review deals with sulfur-containing organic natural products from marine organisms. It includes a survey of selected sulfur-containing primary metabolites and biochemical transformations believed to be of importance in the following discussions of sulfur-containing secondary metabolites of marine origin. The main text deals with about 90 naturally occurring sulfur compounds isolated from marine organisms. Spectroscopic details are reported for most of these compounds and data on their biological activity have been discussed if available. Synthetic approaches to these structures are dealt with. The origin of the metabolites has been critically evaluated. The bulk of structures treated contains reduced sulfur, but examples of compounds with sulfur in higher oxidation states are also given. For comparative purposes numerous natural products of terrestrial or freshwater origin have been included as have some non-sulfur compounds when appropriate. Special sections on life under extreme conditions and future perspectives on sulfur-containing marine natural products research serve to place the topic in a broader perspective. A total of 291 structures and 344 references from the current literature are recorded.