Technological systems are vulnerable to faults. Actuator faults reduce the performance of control systems and may even cause a complete break-down of the system. Erroneous sensor readings are the reason for operating points that are far from the optimal ones. Wear reduces the efficiency and quality of a production line. In most fault situations, the system operation has to be stopped to avoid damage to machinery and humans. As a consequence, the detection and the handling of faults play an increas­ ing role in modern technology, where many highly automated components interact in a complex way and where a fault in a single component may cause the malfunction of the whole system. Due to the simultaneously increasing economic demands and the numerous ecological and safety restrictions to be met, high dependability of technological systems has become a dominant goal in industry in the recent years. This book introduces the main ideas of fault diagnosis and fault-tolerant control. It gives a thorough survey of the new methods that have been de­ veloped in the recent years and demonstrates them by application examples. To the knowledge of the authors, all major aspects of fault-tolerant control are treated for the first time in a single book from a common viewpoint.