Ajax may refer to:
- Ajax (mythology), son of Telamon and a hero in the Trojan war, also known as "Ajax the Great"
- Ajax the Lesser, son of Oileus and also a hero in the Trojan war
- AFC Ajax, a football club from Amsterdam, The Netherlands
- Ajax America, also known as Ajax Orlando, an American soccer team from Orlando, Florida
- Ajax Cape Town FC, a South African football club
- Ajax Kenitra, a Moroccan futsal (indoor football) club
- FC Ajax Lasnamäe, an Estonian football club
- Rabat Ajax, a Maltese football club
- Ajax Sportman Combinatie (ASC), a cricket and football club in Leiden, The Netherlands
- Aias Salaminas F.C., a football club based in Salamina, Greece birthplace of Ajax the Telamonian
- Unión Ájax, a football club in Trujillo, Honduras
- Ajax Heroes, a danish handball team
- Ajax (1906 automobile), Aigner, Switzerland
- Ajax (1913 automobile), Briscoe, France
- Ajax (1914 automobile), Seattle, Washington, U.S.
- Ajax (1921 automobile), prototype, U.S.
- Ajax (American automobile), Nash Motors, 1925–1926, U.S.
- Ajax Electric (automobile), electric, U.S., introduced 1901 in New York
- HMS Ajax, several ships of the Royal Navy
- USS Ajax, several ships of the United States
- Ajax (1860 locomotive), one of the eight South Devon Railway Dido class steam locomotives, in service 1860-1884
- Ajax (1927 locomotive), a LMS Royal Scot Class express locomotive, in service 1927-1962
- Ayaks, a Soviet top secret aerospacecraft project
- Ajax (Sophocles), one of the seven surviving plays by the ancient Greek tragedian Sophocles
- Ajax (Disney), a fictional company (the Disney equivalent of Looney Tunes' Acme Corporation)
- Ajax Duckman, a character in the animated television series Duckman
- Martian Manhunter, a comic superhero called Ajax in Brazil and Portugal
- Ajax (comics), the name of two fictional characters from the Marvel Universe
- Ajax Calkins, a character in Destiny's Orbit and Destination Saturn by Donald Wollheim
- Ajax (Dune), one of the 20 cyborg titans who ruled mankind in the Legends of Dune novels by Brian Herbert and Kevin J. Anderson before Omnius the Evermind gained control.
- War rocket Ajax - From the film Flash Gordon
- Ajak, another Marvel Comics character, a member of the Eternals, sometimes known as "Ajax the Greater"