Russia is getting another five S-400 (also known as the Triumf/Triumph or SA-21) missile battalions in the next year. Russia already has two battalions, with the first one entering service two years ago. Belarus is buying the S-400, and part of a battalion was sent to the North Korean border recently (to make a political point, not that the Russians fear a missile attack from North Korea any time soon.) Within the next six years, Russia plans to buy 18 S-400 battalions, while exporting as many as possible.
An S-400 battalion has eight launchers, each with four missiles, plus a control center and radar. The first one was deployed around Moscow. The Russians claim that this new system can detect stealth aircraft, implying that the hypothetical enemy is the United States. Russia also claims the S-400 can knock down short range ballistic missiles (those with a reentry speed of up to 5,000 meters a second, in the same way the similar U.S. Patriot system does.)
S-400 has a longer range (at 400 kilometers) than Patriot (70 kilometers). Export efforts are hobbled by a lack of combat experience for the system. Patriot has knocked down aircraft and ballistic missiles, S-400 has not. Moreover, Russia anti-aircraft missile systems have a spotty history (especially when confronted by Western electronic countermeasures.) But Russia is already touting a new, S-500 system, that can knock down longer range ballistic missiles (with higher reentry speeds) and stealth aircraft. The missiles around Moscow are part of a project to rebuild the Soviet era air defense system, which has fallen apart since the early 1990s. The new air defense system will be completed in about eight years. The S-500 will be available before that.