The militarisation of space involves the placement and development of weaponry and military technology in outer space. The early exploration of space in the mid-20th century had, in part, a military motivation, as the United States and the Soviet Union used it as an opportunity to demonstrate ballistic-missile technology and other technologies having the potential for military application. Outer space has since been used as an operating location for military spacecraft such as imaging and communications satellites, and some ballistic missiles pass through outer space during their flight. As of 2018, known deployments of weapons stationed in space include only the Almaz space-station armament and pistols such as the TP-82 Cosmonaut survival pistol.

Anti-satellite weapons (ASAT) are space weapons designed to incapacitate or destroy satellites for strategic or tactical purposes. Although no ASAT system has yet been utilized in warfare, a few countries have successfully shot down their own satellites to demonstrate their ASAT capabilities in a show of force. ASATs have also been used to remove decommissioned satellites.