ALKYDS ARE SYNTHETIC POLYMERIC MATERIALS that have been used in the coating industry since the 1930s. Today, they continue to be workhorse polymers for the paint, coating, and printing ink industries. Alkyds and chemically modified alkyd resins are the condensation products of poly-basic acids and polyhydric alcohols. They are used in liquid organic coatings for the architectural, industrial, automotive, and industrial maintenance markets. Alkyds are also known as oil-modified polyesters because of the presence of vegetable or marine oils or other fatty acids. These oils are coreacted into the polyester backbone. The type of oil or fatty acid present in the alkyd contributes to its oxidative cure characteristics. In a chemical sense, alkyds are polyesters that are formulated with drying or nondrying oils. In contrast, polyesters are oil free. Alkyds are often modified with other polymeric materials for particular property attainment. Three major classifications of alkyds are those designed for conventional solids, higher solids, and water-borne coatings. Because there are a large variety of commercially available intermediates and chemical modifiers, i.e., monomers, for the preparation of alkyds, they continue to be a very versatile type of polymers for coatings and printing inks. Most alkyds are film-forming polymers with a relatively low glass transition temperature (Tg ), i.e., below 0°C. They have inherently excellent pigment wetting characteristics and readily accept additives to form coatings with a wide range of appearance, performance, and application characteristics. Alkyds and modified alkyds have a good combination of hardness and flexibility, very acceptable corrosion resistance, good gloss retention, good adhesion to ferrous and nonferrous metals, and other properties that make them acceptable for use on wood, metal, plastic, composite, and other substrates. They are used in areas such as architectural coatings, automotive under-body and under-hood coatings, coil coatings, drum and metal container coatings, electrical insulating enamels, exterior trim paints, maintenance paints, and similar end uses. Alkyd technology has generally evolved slowly over the past few decades. The past few years have shown that technology advances have been made to (a) increase the performance of higher solids alkyds, (b) develop new methods for delivering alkyds in water, and (c) around blend and hybridization science involving other chemistries. Polyesters used in coatings are reaction products of polyhydric alcohols and polybasic acids. Synthetic formulators have the luxury of selecting a variety of multifunctional reactants depending on end use applications, required economics, and coating performance needs.