Caviar or caviare is a food consisting of salt-cured roe of the family Acipenseridae. Caviar is considered a delicacy and is eaten as a garnish or spread. Traditionally, the term caviar refers only to roe from wild sturgeon in the Caspian Sea and Black Sea (beluga, ossetra and sevruga caviars). The term caviar can also describe the roe of other species of sturgeon or other fish such as paddlefish, salmon, steelhead, trout, lumpfish, whitefish, or carp.

The roe can be fresh (non-pasteurized) or pasteurized, which reduces its culinary and economic value.

According to the Food and Agriculture Organization of the United Nations (FAO), roe from any fish not belonging to the family Acipenseridae are not caviar, but "substitutes of caviar". In contrast, the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) defines caviar more broadly, covering the processed roe of all species within the order Acipenseriformes, which includes both sturgeons and paddlefish.

The term caviar is sometimes used to describe dishes that are perceived to resemble caviar, such as "eggplant caviar" (made from eggplant) and "Texas caviar" (made from black-eyed peas).

The term caviare or caviar was first introduced into the English language in the late 16th century and appears to have been borrowed from a number of European languages at the same time, including French cavial, Italian caviale, Portuguese caviar, and Spanish cabial, all of which are ultimately derived from Persian khāvyār (خاویار). Up to the 17th century, archaic spellings included chauiale, cavery, and cauiarie, and as early as 1625, it was becoming a three-syllable word, with the final "e" being dropped in speech. In Russian, the term for caviar is ikra (икра), a term that was used in the English language in the 16th and 17th centuries as ikary.

Caviar and sturgeon from the Sea of Azov began reaching the tables of aristocratic and noble Greeks in the 10th century, after the commencement of large-scale trading between the Byzantine Empire and Kievan Rus'. The Russians likely learned to process fish eggs with salt from Greek traders who had passed along the Black Sea coast, but it was not until after the Mongol invasions that the caviar industry developed in Astrakhan. Production was for a long time centered on the Caspian Sea, with the Iranians and Russians accounting for most of its output.

In the 16th century, François Rabelais described caviar as the finest item of what is now called hors d'oeuvre. By 1569, the Russians had conquered the entire Volga River to its mouth. The Volga and its tributaries offered a diverse range of fish, including sturgeon and its caviar, as well as sterlets, a type of small sturgeon that pleased both Russian locals and foreigners.

Caviar was eaten differently in the past compared to today. Medieval Russians often ate it hot. The Travels of Olearius in Seventeenth-Century Russia says "they expel the roe from the membrane in which it is contained, salt it, and after it has stood for six to eight days, mix it with pepper and finely chopped onions. Some also add vinegar and country butter before serving it. It is not a bad dish. If one pours a bit of lemon juice over it, instead of vinegar, it gives a good appetite, and has a restorative effect."