A moonbase (or lunar base) is a human outpost on or below the surface of the Moon. More than a mere site of activity or temporary camp, moonbases are extraterrestrial bases, supporting robotic or human activity, by providing surface infrastructure. Missions to the Moon have realized single-mission bases, (Tranquility Base being the first), as well as some small permanent infrastructure like lunar laser ranging installations.

Plans for establishing moonbases, with surface or sub-surface research stations, have been proposed and are actively pursued nationally and increasingly internationally. As of 2025, the two most advanced projects to set up moonbases have been pursued multilaterally as part of the US-led Artemis program, with its planned Artemis Base Camp and as the China-led International Lunar Research Station. A broader, international infrastructure has been envisioned with the so-called Moon Village concept, and a general international regulatory regime for lunar activity has been called for by the 1979 signed Moon Treaty, and advocated for with an implementation agreement since 2020.

The surface infrastructure of a base may consist of pre-integrated basic landers, as supporting stations for robotic rovers, or habitation modules for crewed presence, or of surface assembled or in-situ derived and constructed surface stations for sustained lunar habitation. Lunar bases may work with lunar space stations, which in contrast provide infrastructures in lunar orbit supporting activity from there, as with the planned Lunar Gateway of the Artemis program.

The development of moonbases into permanent extraterrestrial settlements has been put forward. Broader lunar colonization or space colonization in general, particularly as laying territorial claims, which is prohibited by international space law, has been criticized for perpetuating colonialism.

The Apollo Program established the first six temporary bases on the Moon, starting with Tranquility Base (1969).

Later robotic missions set up simple robotic temporary bases, leaving their landers behind, starting with Luna 16 (1970).

The 1967 Outer Space Treaty defines the Moon and all outer space as the "province of all mankind". It restricts the use of the Moon to peaceful purposes, explicitly banning military installations and weapons of mass destruction. A majority of countries are parties of this treaty.

The 1979 Moon Agreement was created to elaborate on the Outer Space Treaty, restricting the exploitation of the Moon's resources, particularly by any single nation, leaving it to a yet unspecified international regulatory regime. As of January 2020, the Moon Agreement has been signed and ratified by 18 nations, none of which have human spaceflight capabilities.