ACS is a TLA that may stand for:

• Action Code Script (HeXen game)
• Acute coronary syndrome (see also cardiology)
• Adaptive Comfort Standard , from ASHRAE
• Administrative command system
• Advanced Camera for Surveys (Hubble Space Telescope)
• Alternative Compensation System
• Advanced Computing Systems
• Aerial Common Sensor, from Lockheed Martin
• Affiliated Computer Services Inc. (their stock symbol)
• Agency Computer Systems Inc.
• Alaska Communications Systems
• American Camellia Society
• American Canal Society
• American Cancer Society
• American Cannabis Society
• American Carbon Society
• American Carousel Society
• American Ceramic Society
• American Cetacean Society
• American Cheese Society
• American Chemical Society (acs.org)
• American Clematis Society
• American Cockatiel Society
• American College of Sofia (acs.bg)
• American College of Surgeons
• American Colonization Society
• American Community Schools of Athens (acs.gr)
• American Community Schools, England
• American Community Survey (US Census)
• American Conifer Society
• American Constitution Society
• American Cryonics Society
• Anglo-Chinese School, Singapore
• Apolyton Civilization Site
• Army Community Service (US)
• Associated Colleges of the South (US)
• Association for Canadian Studies
• Association of Caribbean States
• Australian Cinematographers Society
• Australian Computer Society (acs.org.au)
• Australian Correspondence Schools (acs.edu.au)
• Australian Customs Service (customs.gov.au)
• Automobil Club der Schweiz (acs.ch)
• Auxiliary Crane Ship (US Navy hull classification symbol)