Yogurt, yoghurt, or yoghourt (/ˈjoʊɡərt/ or /ˈjɒɡət/; from Turkish:yoğurt; other spellings listed below) is a food produced by bacterial fermentation of milk.

The bacteria used to make yogurt are known as "yogurt cultures". Fermentation of lactose by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and characteristic tang. Cow's milk is commonly available worldwide, and, as such, is the milk most commonly used to make yogurt. Milk from water buffalo, goats, ewes, mares, camels, and yaks is also used to produce yogurt where available locally. Milk used may be homogenized or not (milk distributed in many parts of the world is homogenized); both types may be used, with rather different results.