In many cultures, especially in the West, humans continue to consume milk beyond infancy, using the milk of other mammals (especially cattle, goats and sheep) as a food product. Initially, the ability to digest milk was limited to children as adults did not produce lactase, an enzyme necessary for digesting the lactose in milk. People therefore converted milk to curd, cheese, and other products to reduce the levels of lactose. Thousands of years ago, a chance mutation spread in human populations in northwestern Europe that enabled the production of lactase in adulthood. This mutation allowed milk to be used as a new source of nutrition which could sustain populations when other food sources failed. Milk is processed into a variety of products such as cream, butter, yogurt, kefir, ice cream and cheese.

Humans first learned to consume the milk of other mammals regularly following the domestication of animals during the Neolithic Revolution or the development of agriculture. This development occurred independently in several global locations from as early as 9000–7000 BC in Mesopotamia[24] to 3500–3000 BC in the Americas.[25] People first domesticated the most important dairy animals – cattle, sheep and goats – in Southwest Asia, although domestic cattle had been independently derived from wild aurochs populations several times since

Aside from cattle, many kinds of livestock provide milk used by humans for dairy products. These animals include water buffalo, goat, sheep, camel, donkey, horse, reindeer and yak.

Milk is an emulsion or colloid of butterfat globules within a water-based fluid that contains dissolved carbohydrates and protein aggregates with minerals.[89] Because it is produced as a food source for the young, all of its contents provide benefits for growth. The principal requirements are energy (lipids, lactose, and protein), biosynthesis of non-essential amino acids supplied by proteins (essential amino acids and amino groups), essential fatty acids, vitamins and inorganic elements, and water.

Cream is a dairy product composed of the higher-fat layer skimmed from the top of milk before homogenization. In un-homogenized milk, the fat, which is less dense, eventually rises to the top. In the industrial production of cream, this process is accelerated by using centrifuges called "separators". In many countries, it is sold in several grades depending on the total butterfat content. It can be dried to a powder for shipment to distant markets, and contains high levels of saturated fat.

Buttermilk is a fermented dairy drink. Traditionally, it was the liquid left behind after churning butter out of cultured cream. As most modern butter in Western countries is not made with cultured cream but uncultured sweet cream, most modern buttermilk in Western countries is cultured separately. It is common in warm climates where unrefrigerated milk sours quickly. Buttermilk can be drunk straight, and it can also be used in cooking. In making soda bread, the acid in buttermilk reacts with the raising agent, sodium bicarbonate, to produce carbon dioxide which acts as the leavening agent. Buttermilk is also used in marination, especially of chicken and pork.

Kefir (/kəˈfɪər/ kə-FEER; alternative spellings: kephir or kefier; Russian: кефир [kʲɪˈfʲir]; Karachay-Balkar: гыпы) is a fermented milk drink similar to a thin yogurt or ayran that is made from kefir grains, a specific type of mesophilic symbiotic culture. It is prepared by inoculating the milk of cows, goats, or sheep with kefir grains. Kefir is a common breakfast, lunch or dinner drink consumed in countries of western Eurasia. Kefir is consumed at any time of the day, such as alongside European pastries like zelnik (zeljanica), burek and banitsa/gibanica, as well as being an ingredient in cold soups.

Yoghurt from Ottoman Turkish: یوغورت, romanized: yoğurt; also spelled yogurt, yogourt or yoghourt) is a food produced by bacterial fermentation of milk. Fermentation of sugars in the milk by these bacteria produces lactic acid, which acts on milk protein to give yogurt its texture and characteristic tart flavour. Cow's milk is most commonly used to make yogurt. Milk from water buffalo, goats, ewes, mares, camels, and yaks is also used to produce yogurt. The milk used may be homogenized or not. It may be pasteurized or raw. Each type of milk produces substantially different results. Yogurt is produced using a culture of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus bacteria. Other lactobacilli and bifidobacteria are sometimes added during or after culturing yoghurt.