L4

L4 or L-4 may refer to :

Transportation

 * SP&S Class L-4, an 1884 steam locomotives class
 * USS L-4 (SS-43), a 1915 United States Navy L-class submarine
 * HMS L4, a 1918 British L class submarine
 * Lawson L-4, a 1924 American unflown biplane airliner
 * Piper Cub (U.S. military designation: L-4), an aircraft
 * Inline-four engine (L4), a type of inline internal combustion four cylinder engine
 * Liberty L-4, a World War I four-cylinder, water-cooled, inline, aero-engine
 * Lynx Aviation (IATA code)
 * L4 (New York City bus), a temporary bus route in New York City
 * L4 Westmead & Carlingford Line, a light rail service in Parramatta, Sydney, Australia
 * Chaika L-4, a Russian twin-engined amphibious aircraft
 * Soviet submarine L-4

Science and technology

 * L4 microkernel family, a family of operating system kernels
 * L4, the transport layer in the OSI model of computer communications
 * L4, the fourth Lagrangian point in an astronomical orbital configuration
 * L4, an Lp space for p=4 (sometimes called Lebesgue spaces)
 * L-4, the fourth iteration of L-carrier, high capacity frequency division multiplex over coaxial cable used by the Bell System

Biology

 * Haplogroup L4 (mtDNA), a human mitochondrial DNA haplogroup
 * Ribosomal protein L4, a human gene
 * L4, a lumbar vertebra of the vertebral column, in human anatomy
 * The fourth and last larval stage in the Caenorhabditis elegans worm development

Other uses

 * L4, a modern version of the Bren light machine gun in the British Army
 * ISO/IEC 8859-4 (Latin-4), an 8-bit character encoding