This monograph is devoted to methods of reduction of nonlinear control systems to a simpler form: for example, decomposition into systems of lesser dimension. The approach centres on the immersion of control systems into some differential geometric category. Within the framework of this category the reduction of control systems becomes a reduction to isomorphic objects, quotient objects, and subobjects. The theory of reduction of nonlinear control systems discussed here outlines the elements of the general theory of such systems, which is of necessity purely differential geometric by nature. Audience: This book will be of interest to graduate students as well as to researchers who wish to gain insight into the modern differential geometric theory of nonlinear control systems.