This chapter presents the ubiquitous nature and pervasiveness of lipid oxidation ex vivo in foods and in vivo, and demonstrates that oxidation generally has deleterious results in both systems. This dramatizes the need for more effective strategies for controlling lipid oxidation, both in food materials and in tissues in vivo. The chapter discusses the existing practices using antioxidants, chelators, enzyme inactivation, and anoxic and low-temperature storage conditions. The oxidative degradation of the unsaturated fatty acid components of food lipids may be beneficial in some foods in generating low levels of desirable flavorful carbonyl compounds. However, in general, oxidation causes deleterious changes in flavor, taste, color, texture, and possibly safety of foods. The polyunsaturated fatty acids (PUFA)—particularly the trienoic, pentaenoic, and hexaenoic PUFA commonly found in oilseeds and seafoods—render these foods, which are particularly sensitive to oxidative changes which limit their self-life.