U2 can mean:

• The rock group U2
• The Lockheed U-2 spy plane
  • The U-2 Spy Plane Crisis of 1960
• Unterseeboot 2, German submarine
• The Polikarpov U-2 (Po-2) biplane
• The U2 electric guitar by Danelectro, a 1956 twenty-two fret single-cutaway with two single-coil pickups
• The Siemens-Duewag U2, a light rail vehicle
• The U2 Clothing store
• the song "U2" by the band Negativland, which caused a lawsuit between them and the rock band of the same name
• The Berlin U-Bahn line U2
• The Wien U-Bahn line U2
• one of the IATA codes for EasyJet