X3 may refer to:
Arts, entertainment, and media Films X-Men: The Last Stand, also known as X3 and X-Men 3, the third film in the comic book film series XXX: Return of Xander Cage, a 2017 American film directed by D. J. Caruso
Literature and publications X3, a collection of three science fiction novellas by Gary A. Braunbeck
Music X3 (group), a short-lived Australian girl group, circa 2000 X3 (album), a 2004 solo album by Japanese pop singer Aya Matsuura
Video games X-Men: The Official Game, a 2006 videogame prequel to X-Men: The Last Stand X³: Reunion, a space simulation computer game X³: Terran Conflict, a sequel to X³: Reunion X³: Albion Prelude, an addon to X³: Terran Conflict Dance Dance Revolution X3, a 2011 music video game by Konami Mega Man X3, a 1995 platforming game in Capcom's Mega Man X series
Electronics Instruments Korg X3, a synthesizer
Phones Kyocera X3, an Android One smartphone by Kyocera Mobile phone models by Nokia Nokia X3-00 or Nokia X3 Nokia X3 Touch and Type or Nokia X3-02
Sensors Foveon X3 sensor, a layered image sensor design
Mathematics, science, and technology Astronomy Cygnus X-3, a binary x-ray source in the sky
Computer science X3, one former name of a subcommittee of ANSI, now International Committee for Information Technology Standards (INCITS) X3 (code) aka Excess-3, a binary code also termed Stibitz code XKO X3, an ERP software
Mathematics X3, the mathematical cubic function
Transportation Aircraft Douglas X-3 Stiletto, an experimental jet aircraft Eurocopter X3, an experimental compound helicopter
Automobiles Beijing X3, a Chinese subcompact crossover SUV BMW X3, a German compact SUV Cowin X3, a Chinese compact SUV Geely Vision X3, a Chinese subcompact crossover Jingyi X3, a Chinese subcompact crossover
Bus routes X3 (New York City bus) X3, a Metrobus route in Washington, D.C. U.S.
IATA codes TUI fly Deutschland (IATA airline designator X3 since 2007) Hapag-Lloyd Express (IATA airline designator X3, 2002-2007)
Motorcycles Ilmor X3 (also termed the X³), a MotoGP race motorbike
Spacecraft X-3, the Prospero (satellite) launched by the UK in 1971
Trains X3 (train), a Swedish train built by Alstom
Watercraft HMS X3, an X-class submarine of the Royal Navy
See also 3X (disambiguation)