This book systematically introduced the theory and application of Multidisciplinary Design Optimization (MDO) of flight vehicles. The MDO theory part includes the background, theoretical fundamentals, MDO-oriented modeling, traditional machine learning methods and deep learning-based approximation, sequential approximation modeling, sensitivity analysis, optimization search strategies, MDO optimization procedure, and uncertainty-based MDO. The MDO application covers both subsystem and system examples, including MDO of satellite inner instrument layout design, structural topology optimization, satellite system design, on-orbit servicing task optimization, and MDO of missile and aircraft. This book is characterized by the novelty and practicality with abundant contents, and it is written in an easy way for new learners. It is used by researchers and engineering designers who are engaged in design of flight vehicles or other complex industrial systems. And it is also used as textbook for graduate or undergraduate students majoring in flight vehicle design or related disciplines.