• Australian Capital Territory, the capital territory of the Commonwealth of Australia
• ACT (examination), a college entrance exam in the United States

In business:

• Advanced Cell Technology, a biotech corporation involved in researching and developing cloning and stem cell technologies.
• Ada Core Technologies, a software company that develops an Ada compiler, tools and libraries
• Applied Computer Techniques, a computer services company, renamed Apricot Computers in 1985
• Aviation Composite Technology, an aircraft manufacturer in the Philippines
• ACT (Nasdaq), Automated Confirmation of Transactions, a trade reporting and clearing system
• Asia Container Terminals Ltd.

• Act of Parliament (Act of Congress in the USA) a statute or law passed by a legislature.
• Act (band), a British band
• Act (document), a document recording the legality of a transaction or contract
• Act (theater), a segment of a performance, such as a play or opera
• Acting, action of an actor in a theatrical performance
• ACT (examination), a college entrance examination
• ACT! is a customer relationship management (CRM) application
• Act (web browser), a type of web browser
• Australian Capital Territory, Australian seat of government
• Advanced Concepts Team, A Research Team of the European Space Agency
• Acceptance and Commitment Therapy, A psychological intervention
• Australian Cricket Team
• Act or S-act, the action of a monoid on a set, or a semiautomatonoun

The Acts of the Apostles is a book of the Bible, which now stands fifth in the New Testament. It is commonly referred to as simply Acts. The title "Acts of the Apostles" (Greek Praxeis Apostolon) was first used by Irenaeus in the late second century, but some have suggested that the title "Acts" be interpreted as the "Acts of the Holy Spirit" or even the "Acts of Jesus", since 1:1 gives the impression that Acts is set forth as 'an account of what Jesus continued to do and teach', Christ himself being the principal actor.