S400

S400 may refer to :
 * S-400 missile system, a Russian anti-aircraft weapon system
 * S400 (rocket engine), an ArianeGroup rocket engine
 * Canon S400, a camera
 * PV-S400 Plus, a Casio Pocket Viewer
 * S400, or FireWire 400 computer port
 * Mercedes-Benz S400 BlueHYBRID, a car