This book is dedicated to a new perspective of control systems design, based mainly on the relevance of disturbances. Under the umbrella of engineering science, this book on engineering cybernetics is set in the background and context of modern control theory, which has undergone over half a century of development, as a branch of applied mathematics. While it is a common belief that modern control theory is a natural and necessary growth out of engineering cybernetics, this has proved problematic. This book strives to reconstruct engineering cybernetics by returning to its root problems, premises, aims, and constraints. It is a book of principles and tools that engineers can fully understand and utilize, laying down the foundation for a new kind of control theory, while exposing the pressing needs for theoretical development over the next half century. Engineering cybernetics was also seen as a new paradigm of active disturbance rejection control (ADRC), which has been adopted as a new kind of industrial control technology by industry giants such as Texas Instruments, FreeScale Semiconductors and Parker. The growth of this technology has been explosive and there are no publications currently available on the market.