The letters WW may refer to:
- Bmibaby IATA airline code
- Winchester and Western Railroad reporting mark
- William H. Webster, a director of the FBI and CIA, referred to in the Kryptos sculpture as "WW"
- an abbreviation for whitewater in the International Scale of River Difficulty
- World war, a term for a military conflict affecting the majority of the world
- "Wrong word" in proofreading
- the car number plate code for Wicklow, Ireland
In entertainment:
- WW (album), a 2005 album by the Norwegian metal group Gehenna