3/3 is an infantry battalion in the United States Marine Corps.
3/3 may also refer to:
- 3/3 Lahore Attacks, a 2009 attack on the Sri Lanka national cricket team
- March 3, the 62nd day of most years in the Gregorian calendar
- 3/3, an early band by Japanese musicians Reck and Chiko Hige of the Contortions and Friction fame.