Jax can refer to:
- Jacksonville, Florida, USA, is nicknamed Jax.
- Naval Air Station Jacksonville, nicknamed NAS Jax
- Jacksonville International Airport, IATA Airport Code is JAX
- Jax, Haute-Loire, France, a commune in Haute-Loire
- Jackson Laboratory, one of the world's premiere biology research centers.
- Jackson "Jax" Teller, a character from the TV show Sons of Anarchy.
- Jax Briggs, a fictional character in the arcade/videogame series Mortal Kombat
- Portland LumberJax, an NLL team based in Portland, Oregon
- Java API for XML, an API for the Java programming language
- Jasper Jacks, a character on General Hospital played by Ingo Rademacher
- Jax is a fictitious character from the comic strip You Can With Beakman and Jax
- Jax, the Grandmaster at Arms, a playable champion character in the action real-time strategy video game League of Legends
- Jax Amnell, from The Law of Nines by Terry Goodkind
- Traditional name for black cats in John o'Groats, Scotland