Eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids are long-chain n-3 polyunsaturated fatty acids that are essential for human health. They play an important role in prevention of heart disease and some cancers. The richest source of EPA and DHA are fish and marine products, but in Poland the consumption of fish is slightly declining. Milk enriched with EPA and DHA could be an alternative and effective means of increasing the consumption of these fatty acids. EPA and DHA could be transferred to milk from a cow’s diet or synthesized from their precursor, α-linolenic acid (LNA). Increasing the dietary supply of EPA and DHA, or LNA, has a limited effect, however, due to the extensive biohydrogenation of these fatty acids in the rumen and low uptake by the mammary gland. Feeding protected sources of n-3 polyunsaturated fatty acids does increase the EPA and DHA content of total fatty acids, although absolute levels are relatively low, and results in an increased concentration of conjugated linoleic acid in milk. Issues that need to be researched include the development of a suitable oil supplement and a reliable means of protecting it from rumen biohydrogenation.