Rumen lipid metabolism largely determines the fatty acid composition of dairy products. As such, milk fatty acids can be used as indicators of ruminal and hence animal health. Control of rumen metabolism might also facilitate the production of dairy products enriched in unsaturated fatty acids for an enhanced human health. These include encapsulation technologies, either in a formaldehyde-protein, gelled protein or solid fat matrix. To better understand the origin of fatty acids in dairy products, the first sections address ruminal metabolism, intestinal digestion, transfer to the mammary gland and fatty acid metabolism in the mammary gland. The chapter then addresses the potential to improve the fatty acid composition of dairy products for enhanced human health, with a particular focus on technologies to protect unsaturated fatty acids from rumen biohydrogenation. Finally, the chapter discusses the use of use variation in the milk fatty acid profile, induced by changes in the ruminal lipid metabolism, for monitoring animal health.