Target tracking is a major task of the surveillance radar systems, which are used by the Air Traffic Management (ATM) in every country. These surveillance tasks, not only for the air traffic but alos for the ground traffic on airports, are of growing importance for controlling the air transportation traffic.This book represents a new improvement to apply the Interacting Multiple Model (IMM) algorithm in a novel multisensor non-cooperative surveillance radar system on airports. This new Near-range Radar Netword (NRN) using the multilateration principle for target localization was developed at the German Aerospace Center (DLR). I is also illustrated in this book that the application of one of the most modern tracking algorithms, IMM algorithm, in the NRN has improved the tracking accuracy.