An alkyd is an ester-based polymer derived from the polycondensation reaction of polyhydric alcohol and polybasic acid. This article provides useful information on the chemistry, production, coating formulations, modification, commercial products, and application methods of alkyd resins. It also provides a section on drying oil, which is used in the manufacture of resins. The article describes the three categories of metals that have been used in drier compounds: primary driers (active or oxidation driers), secondary driers (through-driers), and auxiliary driers. It also provides information on the oil length of an alkyd resin and on solvents, which play a critical role in the formulation and use of the coating. The article concludes with a description of the concerns that a user, specifier, or applicator should be aware of when using alkyd coatings.