Russia began its own satellites early warning system at the end of the 60"s with the development of US-K satellites (known as OKO) to make up for lost time vis-a-vis the USA (MIDAS, VELA, DSP). More than 90 satellites were launched between 1972 and 2003 to build up the satellite constellation of the early warning system. This paper first describes the historic background of development and set-up of the Russia's satellite constellation. The current state of Russia's satellite early warning system is then presented, i.e. the number of satellites supposed to be operational, selected orbits. Operational capabilities are assessed in terms of geometrical visibility, coverage or availability. The last part of this paper gives a quick overview of other early warning systems (in operation or underway) in others countries.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.