Act
- A.C.T
- AC Transit
- AC-T (disambiguation)
- ACT (NASDAQ)
- ACT (audio format)
- ACT (for-profit organization)
- ACT (test)
- ACT Alberta
- ACT Alliance
- ACT Awards
- ACT Music
- ACT New Zealand
- ACT Teachers Partylist
- ACT Theatre
- ACT for America
- ACT-CIS Partylist
- ACT-R
- Academy of Clinical Thyroidologists
- Acceptance and commitment therapy
- Acetylcholine
- Achterhooks
- Act (band)
- Act (document)
- Act (drama)
- Act of Congress
- Act of Tynwald
- Act of parliament
- Act! (Italy)
- Act! LLC
- Acting
- Acting (law)
- Acting rank
- Action for Children's Television
- Activated clotting time
- Acts (album)
- AdaCore
- Addenbrooke's Charitable Trust
- Adoptive cell transfer
- Advance corporation tax
- Advanced Cell Technology
- Advanced Computer Techniques
- Advanced Concepts Team
- Agir (France)
- Air ACT
- Aksorn Charoen Tat
- Alliance for Change and Transparency
- Alliance of Concerned Teachers
- Allied Command Transformation
- Amazon Conservation Team
- America Coming Together
- American Canadian Tour
- American College of Toxicology
- American Conservatory Theater
- Anglican Church in Thailand
- Apple certification programs
- Applied Computer Techniques
- Artemisinin
- Ascot railway station (Berkshire)
- Asian College of Technology
- Assertive community treatment
- Association for Citizenship Teaching
- Association of Cinematograph, Television and Allied Technicians
- Association of Corporate Treasurers
- Atacama Cosmology Telescope
- Atria Convergence Technologies
- Australia national cricket team
- Australian Capital Territory
- Australian Civic Trust
- Australian College of Theology
- Aviation Composite Technology
- Azienda comunale del traffico
- Behavior
- California Air Resources Board
- Canberra
- Chattem
- Courtney Act
- Ford ACT
- Madison County Transit
- Puerto Rico Highways and Transportation Authority
- S-act
- Territories of Australia
- The Act (1989 film)
- The Act (TV series)
- The Act (band)
- The Act (musical)
- The Act (video game)
- The Association of Commercial Television in Europe
- Threonine
- Together for Short Lives
- Tycho-2 Catalogue
- UnoTheActivist
- Waco Regional Airport