OKO is a complex of buildings located on plot 16 in the Moscow International Business Center in Moscow. The site is divided into two sections, 16a and 16b. "OKO" means "eye" in Russian, and is also abbreviation for "united with the basement crystal" ("объединённые кристаллом основания").

Oko ( meaning Eye in old Russian), is a Russian (previously Soviet) missile defence early warning programme consisting of satellites in Molniya and geosynchronous orbits. Oko satellites are used to identify launches of ballistic missiles by detection of their engines' exhaust plume in infrared light, and complement other early warning facilities such as Voronezh, Daryal and Dnepr radars. The information provided by these sensors can be used for the A-135 anti-ballistic missile system which defends Moscow. The satellites are run by the Russian Aerospace Defence Forces, and previously the Russian Space Forces. As of December 2015, it is being replaced by the new EKS system.