Margarine (/ˈmɑːrdʒəriːn/, also UK: /ˈmɑːrɡə-, ˌmɑːrɡəˈriːn, ˌmɑːrdʒə-/, US: /ˈmɑːrdʒərɪn/ ^ⓘ) is a spread used for flavoring, baking, and cooking. It is most often used as a substitute for butter. Although originally made from animal fats, most margarine consumed today is made from vegetable oil. The spread was originally named oleomargarine from Latin for oleum (olive oil) and Greek margarite ("pearl", indicating luster). The name was later shortened to margarine, or sometimes oleo (particularly in the Deep South).

Margarine consists of a water-in-fat emulsion, with tiny droplets of water dispersed uniformly throughout a fat phase in a stable solid form. While butter is made by concentrating the butterfat of milk through centrifugation, modern margarine is made through a more intensive processing of refined vegetable oil and water.

Per US federal regulation, products must have a minimum fat content of 80% (with a maximum of 16% water) to be labeled "margarine" in the United States, although the term is used informally to describe vegetable-oil-based spreads with lower fat content.

Margarine can be used as an ingredient in other food products, such as pastries, doughnuts, cakes, and cookies.

Margarine has its roots in the discovery by French chemist Michel Eugène Chevreul in 1813 of margaric acid. Scientists at the time regarded margaric acid, like oleic acid and stearic acid, as one of the three fatty acids that, in combination, form most animal fats. In 1853, the German structural chemist Wilhelm Heinrich Heintz analyzed margaric acid as simply a combination of stearic acid and the previously unknown palmitic acid.

After the French Emperor Napoleon III issued a challenge to create a butter-substitute from beef tallow for the armed forces and lower classes, Hippolyte Mège-Mouriès invented margarine in 1869. Mège-Mouriès patented the product, which he named "oleomargarine", and expanded his initial manufacturing operation from France, but had little commercial success. In 1871, he sold the patent to the Dutch company Jurgens, which subsequently became part of Unilever. In the same year a German pharmacist, Benedict Klein from Cologne, founded the first margarine factory in Germany, producing the brands Overstolz and Botteram.

The principal raw material in the original formulation of margarine was beef-fat. In 1871, Henry W. Bradley of Binghamton, New York, received US Patent 110626 for a process of creating margarine that combined vegetable oils (primarily cottonseed oil) with animal fats. In 1874, the first commercial cargo arrived in the UK. By the late-19th century, some 37 companies were manufacturing margarine in the US, in opposition to the butter industry, which protested and lobbied for government intervention, eventually leading to the 1886 Margarine Act imposing prohibitive taxes and fees against margarine manufacturers.

Shortages in beef-fat supply, combined with advances by James F. Boyce and Paul Sabatier in the hydrogenation of plant materials, soon accelerated the use of Bradley's method, and between 1900 and 1920, commercial oleomargarine was produced from a combination of animal fats and hardened and unhardened vegetable oils. The Great Depression, followed by rationing in the United States and in the United Kingdom, among other countries, during World War II, led to a reduction in supply of animal fat and butter, and, by 1945, "original" margarine had almost completely disappeared from the market. In the United States, problems with supply, coupled with changes in legislation, caused margarine manufacturers to switch almost completely to vegetable oils and fats by 1950, and the margarine industry was ready for an era of product development.^{[dead link]}