ATR
- ARINC
- ATR (TV channel)
- ATR (aircraft manufacturer)
- ATR (company)
- ATR (song)
- ATR 42
- ATR 72
- ATR.1 certificate
- Absent Teacher Reserve
- Acute transfusion reaction
- Advanced Test Reactor
- Advanced tongue root
- African Traditional Religion
- All That Remains (band)
- Americans for Tax Reform
- Andaman Trunk Road
- Anglican Theological Review
- Answer to reset
- Atar International Airport
- Atari Teenage Riot
- Ataxia telangiectasia and Rad3 related
- Atmore (Amtrak station)
- Atractyloside
- Attenuated total reflectance
- Automatic target recognition
- Autothermal reforming
- Average True Range
- List of auxiliaries of the United States Navy
- Reverse mathematics