During the last 10 years marine organisms have provided a large number of new natural products. Interesting compounds have mainly been derived from macroorganisms such as sponges, ascidians, corals and bryozoans. The number of secondary metabolites from marine microorganisms is smaller, but rapidly increasing. Because of the enormous difficulties involved in harvesting products from marine animals, and the fact that some of the bioactive compounds are produced by associated bacteria, the advantages of sustainable production of bioactive metabolites by bacteria or fungi, under the protection of natural resources, seem to be very attractive for the future. This review describes current progress in the isolation and identification of novel marine microorganisms, the discovery of new secondary metabolites, the biotechnological approaches to overproduce them, as well as the evaluation and characterization of their bioactivity.