U3 or U-3 may refer to:
Transportation
edit- U3, an underground rapid transit line in many major German/Austrian cities:
- Avies (IATA code: U3), an Estonian airline
- Cessna U-3, the military model of the Cessna 310 aircraft
- German submarine U-3, one of several German submarines
- Boeing Customer Code for Garuda Indonesia
Computer technology
edit- U3 (software), a design specification for USB storage, created by U3, LLC
- U3, a speed class for Secure Digital (SD) cards
- U.3, an improvement to the U.2 storage interface standard
Video games
edit- Ultima III: Exodus, a 1983 video game
- Uncharted 3: Drake's Deception, a 2011 video game
Other
edit- U3, an unemployment figure released by the United States Bureau of Labor Statistics
- Small nucleolar RNA U3, a type of non-coding RNA