W9

W9 may refer to:

Transportation

 * Wizz Air UK (IATA code: W9)
 * Air Bagan (former IATA code: W9), a former airline of Myanmar
 * London Buses route W9, England

Other uses

 * Form W-9, used by the US federal government for tax purposes
 * W9, a postcode district in the W postcode area, England
 * W9 (TV channel), a French television channel
 * W9 (nuclear warhead), an American nuclear artillery shell
 * Japanese minesweeper W-9, several ships
 * Niland Geyser (scientific designation), California, US