This introduction presents an overview of the key concepts discussed in the subsequent chapters of this book. The book investigates the problem of guaranteed cost control of discretetime linear systems subject to additive/multiplicative controller gain uncertainties, respectively. An optimal guaranteed cost control design method is presented by using the algebraic Riccati equation technique. It is worth mentioning that the standard optimal control design for the same system can be obtained by modifying the cost function. The numerical example has shown the effectiveness of the proposed design procedures. The book deals with the corresponding non-fragile controller and filter design problems. It aims to obtain convex conditions for the filter design problem with respect to the interval multiplicative parameter variation case, while this problem can be resolved well by using the new proposed method. The simulation examples have also shown the effectiveness of the proposed method.