ADX may refer to:
- Djay Adx
- Abu Dhabi Securities Exchange
- Adams Express Company, stock symbol
- Administrative Maximum prisons in the United States
- United States Penitentiary, Florence ADX, the federal supermax prison in Florence, Colorado
- Average directional movement index, a technical analysis indicator
- ADX (file format), a streamed audio format
- Alpha Delta Chi, a national Christian sorority
- RAF Leuchars, United Kingdom, from its IATA airport code
- Amdo Tibetan language, from its SIL code
Category:Three-letter disambiguation pages
ADX is a lossy proprietary audio storage and compression format developed by CRI Middleware specifically for use in video games; it is derived from ADPCM. Its most notable feature is a looping function that has proved useful for background sounds in various games that have adopted the format, including many games for the Sega Dreamcast as well as some PlayStation 2, GameCube and Wii games. One of the first games to use ADX was Burning Rangers, on the Sega Saturn. Notably, the Sonic the Hedgehog series from the Dreamcast generation up to at least Shadow the Hedgehog have used this format for sound and voice recordings.
On top of the main ADPCM encoding, the ADX toolkit also includes a sibling format, AHX, which uses a variant of MPEG-2 audio intended specifically for voice recordings and a packaging archive, AFS, for bundling multiple ADX and AHX tracks into a single container file.