.cxx is a file extension for C++ files.
CXX may also refer to:
- 120 (number) or CXX in Roman Numerals
- AD 120
- No. 120 Squadron RAF
- Sonnet CXX, a sonnet by William Shakespeare
- Canto CXX, a canto of the epic poem The Cantos by Ezra Pound
- C++, the programming language, alternately rendered as "Cxx"
- CX-X, a cargo plane program that resulted in the Lockheed C-5 Galaxy