Oils and fats consist of triacylglycerols containing a range of fatty acids. Commodity oils are predominant sources of C₁₆–C₁₈ fatty acids (corn, cottonseed, groundnut, linseed, olive, palm, rape, sesame, soybean, sunflower), whereas some contain short- and medium-chain fatty acids (butter, coconut, palm kernel) or long-chain fatty acids (fish, other seafoods, algal, and fungal) in various proportions. Fatty acid and triacylglycerol compositions determine the physical, chemical, and nutritional properties of oils and fats and their uses in both food and nonfood, such as oleochemical manufacture. Fatty acids generally contain only two types of reactive functional groups, the terminal carboxyl and a number of carbon–carbon double bonds. Reaction at, or modification of, these groups is central to their industrial use. Oxidation (particularly oxidative degradation of edible fats), reduction (particularly partial hydrogenation), and reactions used to produce surfactants and oleochemicals (epoxidation, ozonolysis, metathesis, sulfonation, production of nitrogen-containing derivatives) are described. A current concern is the environmental impact of industrial chemistry and new processes that use less solvent, milder conditions, and renewable resources, and that produce less waste are required. Oils and fats are a major renewable resource, and environmental concerns may be met “through the use of enzymes and improved chemical catalysts as alternatives to current technologies.” Novel chemistry of oils, fats, and fatty acid derivatives with potential industrial application is highlighted, particularly by introducing new functionality to the alkyl chain.