Preface The book is a collection of contributions concerning the theories, applications and perspectives of Variable Structure Systems (VSS). Variable Structure Systems have been a major control design methodology for many decades. The term Variable Structure Systems was introduced in the late 1950’s, and the fundamental concepts were developed for its main branch Sliding Mode Control by Russian researchers Emelyanov and Utkin. The 20th Century has seen the formation and consolidation of VSS theory and its applications. It has also seen an emerging trend of cross-fertilization and integration of VSS with other control and non-control techniques such as feedback linearization, flatness, passivity based control, adaptive and learning control, system identification, pulse width modulation, H ∞ geometric and algebraic methods, artificial intelligence, modeling and optimization, neural networks, fuzzy logic, to name just a few. This trend will continue and flourish in the new millennium. To reflect these major developments in the 20th Century, this book in- cludes 16 specially invited contributions from well-known experts in VSS theory and applications, covering a wide range of topics. The first chapter, “First State of VSS: People and Events” written by Vadim Utkin, the founder of VSS, oversees and documents the historical developments of VSS in the 20th Century, including many interesting events not known to the West until now. The second chapter, “An Integrated Learning Variable Structure Control Method” written by Jian-Xin Xu, addresses an important issue regarding control integration between variable structure control and learning control. The third chapter, “Discrete-time Variable Structure Control” co-authored by Katsuhisa Furata and Yaodong Pan, describes the design and analysis of discrete-time variable structure control. The fourth chapter, “Higher-Order Sliding Modes for the Output-Feedback Control of Nonlinear Uncertain Systems” written by Giorgio Bartolini, Arie Levant, Alessandro Pisano and Elio Usai, discusses the properties of higher- order sliding mode and its application to output feedback control tasks. The fifth chapter, “Variable Structure Systems with Terminal Sliding Modes” written by Xinghou Yu and Man Zhihong, suggests the utility of a terminal attractor to improve the convergence performance of VSS in slid- ing modes. The sixth chapter, “Adaptive Backstepping Control” written by Ali Ja- fari Koshkouei, Russell Mills, Allan Zinober, applies the backstepping design method to sliding mode control and combines adaptive mechanism. The seventh chapter, “Sliding Mode Compensation, Estimation and Op- timization Methods in Automotive Control” written by ˙ Ibrahim Haskara,