Marmite (/ˈmɑːrmaɪt/ MAR-myte) is a British savoury spread based on yeast extract invented by the Marmite Food Company in 1902. It is made from by-products of beer brewing (lees) and is produced by the British company Unilever. Marmite is a vegan source of B vitamins, including supplementary vitamin B₁₂. It is traditionally eaten spread thinly on buttered toast.

Marmite is a sticky dark-brown paste with a distinctive, salty, powerful flavour and heady aroma. This distinctive taste is represented in the marketing slogan: "Love it or hate it." Such is its prominence in British culture that Marmite is often used as a metaphor for something that is an acquired taste or polarises opinion. Marmite is commonly used as a flavouring, as it is known for its savoury taste due to its high levels of glutamate (1960mg/100g).

The image on the jar shows a marmite (French: [maʁmit]), a French term for a large, covered earthenware or metal cooking pot. Marmite was originally supplied in earthenware pots but since the 1920s has been sold in glass jars. Marmite's distinctive bulbous jars are supplied by the German glass manufacturer Gerresheimer.

Similar products include the Australian Vegemite (whose name is derived from that of Marmite), the Swiss Cenovis, the Brazilian Cenovit, the long-extinct Argentinian Condibé, the French Viandox [fr], and the German Vitam-R. Marmite in New Zealand has been manufactured since 1919 under licence, but with a different recipe; it is the only one sold as Marmite in Australasia and the Pacific Islands, whereas elsewhere the British version predominates.

The first yeast extract spread was invented during the late 19th century when the German scientist Justus von Liebig discovered that brewer's yeast could be concentrated, bottled and eaten. Initial attempts to manufacture this yeast extract for commercial purposes had little success. This was until 1902, when the Marmite Food Extract Company was formed in Burton upon Trent, Staffordshire, England with Marmite as its main product and Burton as the site of the first factory. The by-product yeast needed for the paste was supplied by Bass Brewery. The initial producers of Marmite found that the yeast produced from British beer did not lend itself to the same treatment as continental yeast, which had different methods of fermentation. New machinery and manufacturing processes were implemented before a satisfactory yeast extract product was ready to market.

By 1907, the product had become successful enough to warrant construction of a second factory at Camberwell Green in London. By 1912, the discovery of vitamins was a boost for Marmite, as the spread is a rich source of the vitamin B complex; with the vitamin B₁ deficiency beriberi being common during World War I, the spread became more popular. British troops during World War I were issued Marmite as part of their rations.

During the 1930s, Marmite was used by the English haematologist and physician researcher Lucy Wills to successfully treat a form of anaemia in mill workers in Bombay (present-day Mumbai), British India. She later identified folic acid as the active ingredient. Marmite was used to treat malnutrition by Suriya-Mal workers during the 1934–35 malaria epidemic in British Ceylon (present-day Sri Lanka). Housewives were encouraged to spread Marmite thinly and to "use it sparingly just now" because of limited rations of the product.

In 1990, Marmite Limited, which had become a subsidiary of Bovril Limited, was bought by CPC International Inc, which changed its name to Best Foods Inc in 1998. Best Foods Inc subsequently merged with Unilever in 2000, and Marmite is now a trademark owned by Unilever.