The object of this monograph is to present some optimal design methods in a certain sense for obtaining linear multivariable feedback systems such that they become insensitive or robust properties. The treatment is mainly confined to linear time- invariant discrete systems with the exception of the sections 3.1 and 3.3 in which it was used linear time-invariant conti- nuous systems. Sensitivity and robust methods for multivariable feedback systems have been extensively studied about the last decade and the successful development has led to a much better under- standing of the performance of insensitive and robust proce- dures. The contribution of this monograph is an improved beha- viour of the feedback systems under the influence of distur- bance, parameter variations and/or nonlinear effects with new design methods. Furthermore, in chapter 3 the reader finds improved necessary and sufficient conditions for robust stabi- lity of the closed-loop system. The authors would like to express their thanks to Mrs. Regina Hade, who typed with great patience our manuscript and Mrs. Monika Thieke who drew the figures and symbols very careful.