This book will be of great interest to students in Mechanical and Aeronautical Engineering field, professional engineers, university professors and researchers in universities, government and industry. It will also be of interest to all researchers involved in theoretical, computational and experimental methods used in wind turbine design and wind energy development. The book is divided into ten chapters which are presented in a logical manner. The content is easy to follow and each chapter has its own conclusions. The innovative nature of this book is in its comprehensive review of state-of-the-art in VAWTs, correlation of existing knowledge base and the more recent developments in understanding the physics of flow associated with the Darrieus type vertical axis wind turbine. The principal theories and aerodynamic models for performance calculations are presented with experimental data, not only from laboratory measurements but also from real prototypes. The unsteady aerodynamics of Darrieus type VAWTs is dealt with in detail in chapter 5. A CFD model based on the streamfunction-vorticity formulation of the Navier-Stokes equations is presented to study the highlight unsteady effects that may influence design and performance. The real essence of the book is in chapter 6 which provides a practical design model for the Darrieus type VAWTs based on the double-multiple-streamtube model, originally developed by the author. Several software programs (e.g. CARDAAV) for performance calculations are described : several rotor geometries, conventional and natural laminar flow airfoils, dynamic stall effects, secondary effects and stochastic wind model. The subsequent chapters present aerodynamic load and performance data from water channel and wind tunnel experiments, the state-of-the-art innovative aerodynamic devices as applied to VAWTs and the future trends in the design of Darrieus type wind turbine. Finally, chapter 10 deals with the environmental and social aspects of wind energy since it is an emerging environmental technology of great impact and value, and not just a commercial venture.