404

404 may refer to:
 * 404 (number)
 * AD 404
 * 404 BC
 * HTTP 404, the HTTP error response status for "Not Found"

Cars

 * Peugeot 404, a large family car
 * Bristol 404, a luxury car
 * Unimog 404, an offroad-capable truck

Highways

 * A404(M) motorway, in England
 * Ontario Highway 404, in Canada
 * Maryland Route 404, in the U.S.
 * List of highways numbered 404

Other uses

 * 404 Error Not Found (film), a 2011 Hindi film
 * Project 404, a United States military mission to Laos during the Vietnam War
 * Alitalia Flight 404, an Alitalia-Linee Aeree Italiane flight that crashed on 14 November 1990 killing all on board
 * Martin 4-0-4, an American pressurized passenger airliner built by the Glenn L. Martin Company
 * Area code 404, a telephone area in Atlanta
 * Section 404 of the 2002 Sarbanes–Oxley Act
 * Room 404 – The Wrong Man, the second room in the 1995 film Four Rooms
 * "404", a song by Ram Jam from the 1977 album Ram Jam
 * "404", a 2018 song by Error