Marine oils are receiving increasing attention as a source of C 20 and C 22 carbon omega-3 polyenoic fatty acids. The provision of preformed EPA and DHA from marine oils has profound implications for health and disease. Their role as precursors for the synthesis of eicosanoids and docosanoids explains many of the multisystemic effects observed when they are administered. Furthermore under some physiologic conditions such as preterm birth the evidence suggests that C 18 omega-3 fatty acids are not sufficiently converted to DHA to allow for biochemical and functional normalcy, thus DHA may be considered a conditionally essential nutrient for normal eye and brain development. Under disease conditions EPA plays a major role in modifying the balance between omega-6 and omega-3 derived eicosanoids thus modulating related functions. The use of marine oils has some potential risks that can be circumvented by careful processing, storing and preserving the unsaturated fatty acids. Technological procedures based on chemical and physical separation of the unsaturated fatty acids has permitted the elaboration of concentrated EPA and DHA for clinical testing. The development of structured lipids has allowed the synthesis of novel forms of EPA and DHA delivery. Further uses of marine oil to optimize health and prevent disease are predicted based on recent knowledge and technological developments.