ATAC, or Atac may refer to:
- Atac, a French supermarket chain
- Asbestos Testing and Consultancy Association, a UK trade association
- American Teens Against Crime, a fictional crime fighting organization in The Hardy Boys Undercover Brothers novel series
- Navy Antiterrorist Alert Center, the 1983–2002 United States Navy terrorism watch center
- Advanced Technology and Academic Centre, a building at Lakehead University's Thunder Bay Campus
- ATAC SpA, the company that provides public transport in Rome, Italy
- Automatic Targeting Attack Communicator, a military communication device in the James Bond movie For Your Eyes Only
- Anti-Terrorist Action Command, a fictional police organization in the 1981 movie Nighthawks
- The ATAC (Arimidex, Tamoxifen, Alone or in Combination) trial was an international randomised controlled trial of 9366 women with localized breast cancer.
- Auto Tension Adjustment Concept, an off-road clipless bicycle pedal system developed by TIME Sport International
- Air Transport Association of Canada, a national trade association for commercial aviation and flight training industries as well as aviation industry suppliers