Assertive Community Treatment, a system for treating mental illness

ACT (cognitive model), a symbolic cognitive architecture

Australian Capital Territory, the capital territory of the Commonwealth of Australia

ACT New Zealand, a political party and movement in New Zealand

Artemisinin-based Combination Therapy, a treatment for malaria

ACT (examination), a college entrance exam in the United States

ACT (audio format) used in some Chinese MP4/MTV players

Acceptance and Commitment Therapy, a type of cognitive-behavioral therapy

Allied Command Transformation, a NATO strategic command

Action for Children's Television, an organization dedicated to improvements in children's television

Applied Computer Techniques, a computer services company, renamed Apricot Computers in 1985

Atacama Cosmology Telescope, a telescope under construction in Chile

Advanced Concepts Team, a research team of the European Space Agency

ACT!, contact management software

American Conservatory Theater, in San Francisco, California

Alliance of Concerned Teachers, an alliance of teachers, educators and teacher organizations in the Philippines

Ascot railway station, a railway station in the United Kingdom with the National Rail code "ACT"

Waco Regional Airport, an airport in Waco, Texas, United States, with the IATA airport code "ACT"

Advanced Cell Technology, a biotech corporation involved in researching and developing cloning and stem cell technologies.

America Coming Together, a United States political group

A.C.T, a progressive rock band from Sweden

Academy of Clinical Thyroidologists

Astrographic Catalog/Tycho, a star catalogue

Association of Cinematograph Technicians

Act (disambiguation)

Association of Corporate Treasurers

Association for Competitive Technology, a pro-Microsoft lobby group

ACT can be abbreviation for activity

Aviation Composite Technology, an aircraft manufacturer in the Philippines

ACT (Nasdaq), Automated Confirmation of Transactions, a trade reporting and clearing system

Ada Core Technologies, a software company that develops an Ada compiler, tools and libraries