AF (or variants) may refer to:

• Anarchist Federation (British Isles), an Anarchist-Communist agitational organisation in Britain
• Air France, IATA airline designator for Air France
• Abercrombie & Fitch, an American based, international clothing retailer
• Alliance française
• A-F Records, a record label
• Acronym Finder
• Alabama and Florida Railway, from its reporting mark
• American Freightways, a trucking company now operating as FedEx Freight East
• Adventist Forums, an organization of progressive Seventh-day Adventists
• AF Gruppen, a multi national construction and development company based in Norway
• ÅF, a Swedish technical consulting company

.af is the Internet country code top-level domain (ccTLD) for Afghanistan. It is administered by AFGNIC, a service of the UNDP and the Islamic Republic of Afghanistan.

ÅF is a Swedish technical consulting company. It was formed in 1895 and is one of the biggest consulting companies in Sweden. ÅF was previously known as Ångpanneföreningen.

Alkaline phosphatase (ALP, ALKP) is a hydrolase enzyme responsible for removing phosphate groups from many types of molecules, including nucleotides, proteins, and alkaloids. The process of removing the phosphate group is called dephosphorylation. As the name suggests, alkaline phosphatases are most effective in an alkaline environment. It is sometimes used synonymously as basic phosphatase.

Alpha Phi (ΑΦ) International Women's Fraternity was founded at Syracuse University on September 18, 1872. Alpha Phi currently has 152 active chapters and over 200,000 initiated members. Its celebrated Founders' Day is October 10. It was the third Greek-letter organization founded for women. In Alpha Phi the Greek letter Phi is pronounced "Fee". It is a common misconception that this pronunciation is because Phi follows the vowel Alpha. However, the pronunciation of Phi as "Fee" rather than "Fi" actually results from the fact that the organization adopted the Greek rather than anglicized, mainly American, pronunciation of the letter because it sounded more feminine.