Omega-3 fatty acids from fish and fish oils are not to be confused with those from plant sources, such as flax and canola oil. These plant oils are enriched in an omega-3 fatty acid called α-linolenic acid, which is a metabolic precursor of the omega-3 fatty acids found in fish and fish oils (Figure 1). Although we are able to convert dietary α-linolenic acid into eicosapentaenoic, docosapentaenoic and docosahexaenoic acids (which are found in fish and fish oils), this conversion is not efficient in people who consume a typical Western diet. Consequently, following the consumption of foods containing α-linolenic acid, our tissues are exposed to very little of the types of omega-3 fatty acids found in fish and fish oils. Some beneficial biological activity has been attributed to plant-derived omega-3 fatty acids; however, the associated health benefits are likely independent of the conversion of α-linolenic acid to the fatty acids found in fish. In addition, dietary oils that are rich in α-linolenic acid do not, for the most part, reproduce the biological activity associated with dietary fish oils.3 The balance of this review will address the types of omega-3 fatty acids typically found in fatty fish and fish-oil supplements.