This is a synchronization focused book prepared on the basis of the completed projects supported by the Natural Science Found Committee of China - "Study on Theory and Its Application of Controlled Synchronization of Mechanical Systems" and "Study on Theory and Its Application of General Synchronization and Intelligent Fixed Speed Ratio Drive Control of Multi-Motors Mechanical Systems", as well as the other relative projects. This book explores vibratory synchronization, controlled synchronization and combined synchronization of two or more motors driven mechanical systems, and fixed speed ratio control, as well as controlled synchronization of multi-hydraulic cylinders based on the theories of non-linear mechanical dynamics, modern and intelligent controls. This book describes in detail the basic principles and methods as well as the concrete measures, and introduces the author's many years' working experiences in the engineering practice during the research of these projects. In this book, theories and methods are illustrated by specific examples relatable to engineering applications. This book is suitable for university or college staff and students as teaching materials or reference books. It is also suitable for the technical professionals who are working on the research and the design of mechanical engineering, automation and dynamics.