This book describes systematically telemetry theory and methods for aircraft in flight test. Test targets of telemetry in flight test include airplanes, helicopters, unmanned aerial vehicles, aerostatics, carrier-based aircraft, airborne equipment (systems), weapon systems, (powered) aircraft scale models, aircraft external stores (e.g., nacelle, auxiliary tanks), and ejection seats and so on. The book collects the author's telemetry research work and presents methods that have been verified in real-world tests. The book has eight chapters: the first three discuss the theoretical basis of telemetry, while the other five focus on the methods used in flight tests. Unlike other professional textbooks, this book describes the practical telemetry theory and combines theory and engineering practice to offer a comprehensive and systematic overview of telemetry in flight test for readers.