ACS is a TLA that may stand for:
- Action Code Script (Hexen game)
- Administrative command system
- Advanced Camera for Surveys (Hubble Space Telescope)
- 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
- 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
- Automobil Club der Schweiz (acs.ch)
- Auxiliary Crane Ship (US Navy hull classification symbol)