This paper describes the multiple target multi-sensor tracking (MST) system that has been developed by CelsiusTech Systems AB for air defense purposes. The kinematic tracking principles are first treated. An interactive multiple model (IMM) filter, together with track oriented multiple hypothesis tracking (MHT) and automatic bias estimation schemes, result in a high overall tracking performance. An arbitrary mix of active and passive measurements can be handled, using advanced Bayesian initiation and deghosting techniques. Moving sensor platforms are allowed and tactical ballistic missile tracking capability is available. The MST system includes integrated functionality for noncooperative target type identification. Recursive and Bayesian techniques are used in order to estimate target type probabilities from a variety of information sources. These include electronic support measures (ESM), infra red search and track (IRST) sensors, direct type observations and the estimated kinematic behavior of the track.