ATG may refer to:
- ATG, the triplet code for the amino acid methionine
- Anti-thymocyte globulin, antibodies to prevent and treat transplant rejection
- ATG Stores, an e-tail site
- Antigua and Barbuda, using its ISO 3166-1 alpha-3 country code
- Alexander the Great, king of Macedon, in northern Greece
- Adhesive Transfer Gun, the formal name for a tape gun
- Advanced Technology Group, a division of Apple Computer
- Alaska Territorial Guard, a military reserve force in World War II
- Alternative Tourism Group, a Palestinian NGO
- Ambassador Theatre Group, a theatre group in the UK
- Anti-tank gun, a mobile weapon used against armoured vehicles
- Anti Tank Guitar, a string instrument
- Art Technology Group, a software developer
- Art Theatre Guild, a Japanese film production company
- At the Gates, a melodic death metal band
- Aviation Technology Group, the defunct developer of the Javelin Very Light Jet (VLJ)