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Chemistry/Biochemistry:

Adenosine triphosphate, the universal energy currency of all living organisms

Companies:

Alberta Theatre Projects, a major Canadian theatre company.

Associated Talking Pictures, a British film company which later became Ealing Studios

BAe ATP, the British Aerospace ATP

ATP Bonding Systems, a British technology company specialising in adhesives.

ATP Flash Cards, American memory card manufacturer known for weatherproof memory.

Organizations

Academic Talent Program

Association of Test Publishers

Association of Tennis Professionals, professional men's tennis association

Advanced Training Program, Youth soccer training program

Technologies

AppleTalk Transaction Protocol

Automated theorem proving

Automatic train protection system

Acquisition, tracking and pointing

Anti-Tachycardia Pacing (see Implantable cardioverter-defibrillator)

Asynchronous Transfer Protocol (telecommunications)

Alternative Transients Program

Other

Airline Transport Pilot License

Flight Assignment: A.T.P., a MS-DOS game

Australian Technology Park

All Tomorrow's Parties, a music festival.

All Tomorrow's Parties, A song by the Velvet Underground, released in 1967 on the album The Velvet Underground and Nico

All Tomorrow's Parties, A novel in the Bridge trilogy by William Gibson

Accepted Test Plan

Addressee To Pay

Adult Treatment Panel, guidelines for patients with high cholesterol

Allmänna tilläggspensionen, a supplementary (income-related) pension in Sweden.

Arbejdsmarkedets Tillægspension, a supplementary (income-related) pension in Denmark

Available To Promise

Ask Them Personally