L4

L4 may refer to:

* L4 microkernel family
* HMS L4, a British L class submarine
* SP&S Class L-4, a 1884 steam locomotives class

; others :
* the fourth Lagrange Point in an astronomical orbital configuration.
* fourth lumbar vertebra of the vertebral column, in human anatomy
* straight-4 engine
* L-4, one of the U.S. military designations for the Piper Cub in World War II
* L4, a modern version of the Bren light machine gun actually in service in the British Army
* The fourth iteration of L-carrier, high capacity frequency division multiplex over coaxial cable used by the Bell System
* Denver, Colorado based Lynx Aviation IATA code