The term L3 may refer to:

• The L3 microkernel, the predecessor of the L4 microkernel family in Computers
• The Level-3 CPU cache in a computer
• The third lumbar vertebra in Human anatomy
• The third Lagrange Point in an astronomical Solar System
• An Italian tank type in WWII Combat Vehicles
• The Russian manned lunar lander design type in the Soyuz space program, or to the related Soyuz L3 Lunar Orbiter (November 23, 1972 Launch Failure)
• Latitude/Longitude Locator, an STS-32 Space Shuttle mission experiment
• An L band Radio Frequency in the Electromagnetic spectrum
• L-3, a company providing Intelligence, Surveillance and Reconnaissance (ISR) systems
• One of the four detectors of the Large Electron-Positron Collider