ALS (Amyotrophic Lateral Sclerosis) is a chronic and fatal form of motor neuron disease; also known as Lou Gehrig's disease in the US, or Charcot's disease in the French-speaking world.

ALS or Als may also refer to:

• Als (island), Denmark

• Airman Leadership School, a U.S. Air Force program
• ALS – Aircraft Leasing Services, a Kenyan airline
• Approach lighting system, an airport runway lighting system
• San Luis Valley Regional Airport, IATA code ALS

• Advanced life support, a level of medical training
• Anterolateral system, part of the nervous system
• Antibodies from lymphocyte secretions, an immunological assay
• Angular leaf spot, a bacterial plant disease

• Acetolactate synthase, an enzyme
• Advanced Light Source, a synchrotron radiation facility
• ALSN, automatic train signalling (автоматична локомотивна сигналізація), a train protection system
• Alternate line service, a mobile phone feature
• Aluminized steel, as used in engineering drawings
• Ammonium lauryl sulfate, a household chemical
• Antilag system, a system used on turbocharged engines
• Audio Lossless Coding, an audio codec
• LS TTL, advanced low-power Schottky
• Photodetector, ambient light sensor
• Alternating least squares, a matrix factorization method

• Als, a nickname used for the Montreal Alouettes of the Canadian Football League
• ALS Association, an American nonprofit organization
• American Littoral Society, an American environmental organization
• Antar Lintas Sumatera, an Indonesian intercity bus company
• Arrowhead Library System (Wisconsin)
• Australian Linguistic Society
• Associated London Scripts, a comedy-writers collective founded by Spike Milligan

• A. Lange & Söhne, a German luxury watch brand
• als, since 2003 prefix for the Wikipedia (als:Wikipedia:Houptsyte) of Alemannic German dialects like Alsatian, Swabian, Swiss German
• als, since 2007 the ISO 639-3 code for the southern Albanian dialect (Tosk Albanian)
• Alternative Learning System (Philippines), a modular non-formal education program
• Associate of the Linnean Society of London
• Auld Lang Syne, a traditional Scottish folk song
• Autographed Letter Signed, a term used by autograph collectors
• Singapore Area Licensing Scheme