Act

• The Act, American rapper also known as UnoTheActivist
• A.C.T, a Swedish band
• Act (band), a British band
• The Act (band), a Norwegian rock band from the 1980s
• Act (drama), a segment of a dramatic or musical work (such as a play, opera, or ballet)
• Acting, theatrical performance
• ACT Music, a German music label
• The Act (musical), a 1977 musical
• The Act (1989 film), a 1989 British television film by Richard Langridge
• Acts, a 2012 album by American band RNDM
• ACT Theatre, in Seattle, Washington, US
• The Act (TV series), a 2019 true crime TV series
• The Act (video game), a 2007 arcade game produced by Cecropia
• American Conservatory Theater, in San Francisco, California, US
• Arts & Culture Trust, a South African cultural organisation responsible for the ACT Awards

• Aviation Composite Technology, an aircraft manufacturer in the Philippines
• IATA airport code for Waco Regional Airport in State of Texas, USA

• AdaCore, formerly Ada Core Technologies, Ada specialist software company
• Advanced Cell Technology, stem cell company
• Advanced Computer Techniques, a U.S. software company 1962–1994
• Applied Computer Techniques, later Apricot Computers, UK
• Atria Convergence Technologies, a telecommunications company in India

• ACT (for-profit organization), provides assessments etc. for US school students etc.
• ACT (test), for college admission, US
• Asian College of Technology, Cebu City, Philippines
• Australian College of Theology

• AC Transit, a transit agency serving Alameda and Contra Costa Counties, California
• Advanced Clean Trucks Regulation, a rule made by the California Air Resources Board which requires trucks to decarbonize
• Advanced Concepts Team, a research team of the European Space Agency
• Agency for Community Transit, a paratransit system for Madison County Transit, Illinois
• Allied Command Transformation, a NATO strategic command
• Azienda comunale del traffico, a former transport operator in Lugano, Switzerland
• Puerto Rico Highways and Transportation Authority ({{langx|es|Autoridad de Carreteras y Transportación|link=no}})

• Act (document), a document recording the legality of a transaction or contract
• Acting (law), someone temporarily exercising the powers of a vacant position
• Act of parliament, Act of Congress, or Act of Tynwald, a statute or law passed by a legislature
• Advance corporation tax, a tax collected in the UK until 1999

• ACT Alberta, a Canadian coalition to raise awareness about human trafficking
• ACT Alliance, an alliance of churches for coordinating humanitarian assistance and development work
• ACT-CIS Partylist, a political party in the Philippines
• ACT for America, an advocacy group in the United States
• Action for Children's Television, an organization dedicated to improvements in children's television
• Act! (Italy), an Italian political party
• ACT New Zealand, a political party in New Zealand
• ACT Teachers Partylist, a political party in the Philippines
• Agir (France) (French for "Act"), a political party in France
• Alliance for Change and Transparency, a political party in Tanzania
• Amazon Conservation Team, a non-profit organization that works to protect the Amazon rainforest
• America Coming Together, a US political group

• Academy of Clinical Thyroidologists, United States
• Alliance of Concerned Teachers, Philippines
• American College of Toxicology
• Association for Citizenship Teaching, UK
• Association of Cinematograph, Television and Allied Technicians, UK
• Association of Corporate Treasurers, UK

• ACT, former name of Together for Short Lives, a children's charity in the United Kingdom
• Addenbrooke's Charitable Trust, a UK charity
• Anglican Church in Thailand
• The Association of Commercial Television in Europe, a group representing the business interests of commercial television in the EU
• Australian Civic Trust, an Australian urban design organization

• Act! LLC, a customer relationship management software
• ACT (NASDAQ), Automated Confirmation of Transactions, a trade reporting and clearing system
• ACT-R, a symbolic cognitive architecture
• Apple Certified Trainer, one of the Apple certification programs

• Acceptance and commitment therapy, a type of cognitive-behavioral therapy
• Acetylcholine, (ACt/ACh) a neurotransmitter
• Activated clotting time, a test of coagulation
• Adoptive cell transfer, transfer of cells into a patient, usually immune system cells
• Artemisinin based combination therapy, a treatment for malaria
• Assertive community treatment, a system for treating mental illness

• ACT, a codon for the amino acid Threonine
• ACT (audio format), a file format
• Act or S-act, the action of a monoid on a set, or a semiautomaton
• Astrographic Catalog/Tycho or Tycho-2 Catalogue
• Atacama Cosmology Telescope, Chile
• Ford ACT, a transit system

• American Canadian Tour, a stock car racing series
• Australia national cricket team

• ACT, the National Rail code for Ascot railway station, Berkshire, UK

• Acting rank, temporary military rank
• {{Smallcaps all|ACT}}, in linguistics, glossing abbreviation for active voice
• ACT mouthwash, produced by Chattem
• ACT, the ISO 639-3 language code for Achterhooks, a Dutch dialect
• Australian Capital Territory ("The ACT"), the territory in which the Australian capital city of Canberra is seated
• Courtney Act, Australian drag queen, singer, and television personality

• AC-T (disambiguation)
• Behavior

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