Lunar Laser Ranging (LLR) measures the distance between the Earth and the Moon using laser ranging. A short pulse of coherent light generated by a laser (Light Amplification by Stimulated Emission of Radiation) is transmitted in a narrow beam to illuminate corner cube retroreflectors on the moon. The return signal, typically a few photons, is collected by a telescope and the time-of-flight is measured. Apollo astronauts and Russian rovers deployed laser ranging retroreflector arrays on the lunar surface which continue to yield fundamental scientific data. Analysis of Lunar Laser Ranging (LLR) data provides information on the lunar orbit, rotation, solid-body tides, and retroreflector locations.