This book introduces robust estimation and failure detection, with a thorough presentation of Kalman filtering and H-infinity filtering theory. These estimation techniques make it possible for engineers to design estimators that are more general and robust. The book also reviews the likelihood ratio method for failure detection and demonstrates how to design failure detectors that are sensitive to failures but insensitive to model variations. This book will give engineers a concise presentation of these important techniques, as well as an overview of important robust control developments of the last fifteen years.