Aldi (stylised as ALDI) is the common company brand name of two German multinational family-owned discount supermarket chains operating over 10,000 stores in 20 countries. The chain was founded by brothers Karl and Theo Albrecht in 1946, when they took over their mother's store in Essen. The business was split into two separate groups in 1960, that later became Aldi Nord, headquartered in Essen, and Aldi Süd, headquartered in Mülheim.

In 1962, they introduced the name Aldi (a syllabic abbreviation for Albrecht Diskont), which is pronounced [ˈaldiː] (listen). In Germany, Aldi Nord and Aldi Süd have been financially and legally separate since 1966, although both divisions' names may appear as if they were a single enterprise with certain store brands or when negotiating with contractor companies. The formal business name of Aldi Nord is Aldi Einkauf GmbH & Co., while the formal business name of Aldi Süd is ALDI SÜD Dienstleistungs-SE & Co. Each company is owned and operated independently, but do have contractual business with one another.

Aldi's German operations consist of Aldi Nord's 35 individual regional companies with about 2,500 stores in western, northern, and eastern Germany, and Aldi Süd's 32 regional companies with 1,900 stores in western and southern Germany. Internationally, Aldi Nord operates in Denmark, France, the Benelux countries, Portugal, Spain and Poland, while Aldi Süd operates in Ireland, the United Kingdom, Hungary, Switzerland, Australia, China, Italy, Austria and Slovenia. Both Aldi Nord (as Trader Joe's) and Aldi Süd (as Aldi) also operate in the United States with 1,600 stores between them as of 2017, and the U.S. is the only country to have both Aldi companies operating outside of Germany.