This volume is intended for engineers in research and development and applied mathematicians. It is also designed to be a useful reference for graduate students in linear systems with interests in control. With this purpose in mind, the discrete-time case is treated in an isomorphic fashion with the continuous-time case. This volume is self-contained: four mathematical appendices develop the many specialized mathematical results needed in the main text. In the development of Linear System Theory emphasis is placed on careful and precise exposition of fundamental concepts and results. The main topics of Linear System Theory are treated systematically: the dynamics of linear time-varying and time-invariant systems; stability; controllability and observability; realizations; linear feedback and estimation; linear quadratic optimal control; finally, the last chapter develops the main results of unity-feedback MIMO systems. At various suitable places basic computational issues and robustness issues are discussed.