The monograph is devoted to the structural synthesis of parallel mechanisms (PM), which is one of the most important tasks in the development and design of a variety of innovative devices based on the use of parallel mechanisms: parallel manipulators, machines with parallel kinematics, moving simulators, tactile devices, micro- and nanomanipulators. The structural synthesis of parallel mechanisms consists in finding all the structures of the PM that implement the required movement. The book contains a classification of PM, an effective method of structural synthesis of PM and a large number of parallel mechanisms suitable for practical use. The approach to synthesis is based on the concept of virtual circuits and the application of the elementary notation of screw theory. With this approach, parallel mechanism families are constructed from a set of composite units. This approach is conceptually simple and convenient. In addition, to simplify the understanding of the architecture of any parallel mechanism, the book provides a generalized procedure for analyzing the mobility of the PM. To read this book, you need only basic knowledge of linear algebra and kinematics. The book is intended for researchers, developers, engineers and graduate students interested in robotics, machine and mechanism design and screw theory.