Recently, the food industry, the agricultural community and consumers have shown a growing interest in the so-called functional food [1–3]. Natural bioactive compounds in some dietary products are claimed to prevent various diseases such as inflammation, degenerative diseases and cancer . This paper reviews molecular structures, nutritional importance and availability of natural bioactive compounds present in vegetable and fish oils. Chapter 1 includes general description of polyunsaturated fatty acids (PUFA's), their physiological role and metabolism in mammalian organisms ([7–20], Schemes 1 and 2, Figs. 1 and 2). There is a link between dietary PUFA intake, inflammation and immunity. A composition of fatty acids in mammalian cells is sensitive to change in the fatty acids diet. The n-6 PUFA’s are the precursors of prostaglandines and related compounds, which play an important role in inflammation and in regulation of immunity. On the contrary, the n-3 PUFA's abundant in fish oils and also present in some plant seed oils have antiinflammatory properties and are therapeutically useful in several diseases. DHA from this family may also exert beneficial effects on development of the nervous system. Irrespective of PUFA's, vegetable oils contain a variety of bioactive compounds, mainly lipid-soluble antioxidants. This class of antioxidants includes vitamin E ([21–37], Figs. 3 and 4), which is a generic term that constitutes a group of structurally related compounds comprising of tocopherols and tocotrienols. A presence of the phenolic hydroxyl group in these compounds is critical for their antioxidant activity and enables to scavenge freeradical species both in vitro and in vivo. Other bioactive compounds present in vegetable oils are plant lignans ( [38–64], Fig. 5). In a human body, the plant lignans are converted to the mammalian lignans enterodiol and enterolactone. In the literature cited, lignans are discussed as anticancer agents, especially against breast and prostate cancer. Apart from a weak estrogenic properties, their anticancer activity may be supported on the antioxidation capacity. Vegetable oils are also a good source of phytosterols ([65–80], Figs. 6 and 7). Despite their similar chemical structures, phytosterols and cholesterol differ markedly from each other in regard to their pharmacological characteristics including intestinal absorption and further metabolism. Phytosterols produce a wide spectrum of therapeutic effects in the human organism including anti-tumor properties. In addition, another compounds present in edible oils are described, e.g. carotens and coenzyme Q10, all of which have potent biological activity, and exert beneficial effects in regard to cardiovascular and cancer diseases ([81–101], Fig. 8). The majority of the bibliography included in the present review is selected from that published since 2000 by the year 2009.