This monograph concerns the design of feedback controllers for multivariable linear dynamic systems. The particular approach is to consider a coprime factor description of the plant's transfer function and to represent a family of systems by perturbing the numerator and denominator. The design of controllers to robustly stabilize such a family is posed as an H? optimization problem and some explicit solutions are obtained. Similarly, procedures for reduced order modelling and controller design are derived. Finally, the results are exploited to give a systematic loop shaping control system...