Aioli , allioli or aïoli ( or ; Provençal Occitan: alhòli [aˈʎɔli] or aiòli [aˈjɔli]; Catalan: allioli [ˌaʎiˈɔli]; Spanish: alioli [ˌaliˈoli]) is a cold sauce consisting of an emulsion of garlic and olive oil; it is found in the cuisines of the northwest Mediterranean, from Andalusia to Calabria.

The names mean "garlic and oil" in Catalan and Provençal. It is found in the cuisines of the Mediterranean coasts of Spain (Catalonia, the Valencian Community, the Balearic Islands, Murcia, and eastern Andalusia), France (Provence), Italy (Sicily and Calabria), and Malta.

Some versions of the sauce are closer to a garlic mayonnaise, incorporating egg yolks and lemon juice, whereas other versions lack egg yolk and contain more garlic. The latter gives the sauce a pastier texture, making it more laborious to produce as the emulsion is harder to stabilise. There are many variations, such as adding lemon juice or other seasonings. In France, it may include mustard. In Malta, arjoli or ajjoli is commonly made with the addition of either crushed galletti (a type of cracker) or tomato.

Like mayonnaise, aioli is an emulsion or suspension of small globules of oil and oil-soluble compounds in water and water-soluble compounds. In Spain, purists believe aioli should not include egg, but in France and elsewhere, egg or egg yolk is the usual emulsifier.

Since about 1990, it has become common in the United States to call all flavored mayonnaises aioli. Purists insist that flavored mayonnaise can contain garlic, but true aioli contains garlic and no other seasoning (except salt).