Austria's ISO, 2-letter country code

Counter-terrorism, also known as "anti-terrorism" (AT)

Alimentary tract

Análisis Transaccional (Spanish "Transactional analysis"), a psychological method

Appalachian Trail

Abel Tasman, a seventeenth century Dutch explorer and merchant

Appropriate Technology

Assistive technology

Aphex Twin

Anti-tank weapons

Ataxia telangiectasia, an immunodeficiency disorder

Automatic transmission

Anguilla, a World Meteorological Organization country code

Hayes command set for computer modems (all commands begin with the characters "AT")

"@", the punctuation symbol now typically used in e-mail addresses

Astatine, the chemical symbol for the element

Atchison County, Kansas (county code)

Royal Air Maroc (IATA airline designator)

attotesla, an SI unit of magnetic flux density

IBM Personal Computer/AT

a subdivision equal to 1/100 of a Kip, the unit of currency in Laos

The common name for the 5-pin DIN keyboard connector

Acceptance test

Ashmore and Cartier Islands (FIPS 10-4 territory code and obsolete NATO country code

Anaerobic threshold

.at is the Internet country code top-level domain for Austria

AT form factor for motherboards and computer cases

Atmel Corporation

at (Unix command), to schedule tasks to be performed at a later date

Audit trail

Attack Team (game), a 2000 computer game

technical atmosphere (symbol), physical unit of pressure

Aarne-Thompson classification system

Ampere-turn (symbol), an International System of Units (MKS) unit of magneto-motive force

Air Trecks, fictional inline skates in the manga and anime Air Gear