The linear quadratic design of an opimal robust servo-controller for a continuous-time control system is described. It introduces a servo- control performance measure which accommodates the internal model principle. The measure selectively discounts penalties on control effort of desirable frequencies and provides complete flexibility in the selection of weighting matrices. The proposed servo-controller uses plant state feedback, signal state feedforward and a servo-compensator for ensuring robust asymptotic command tracking and disturbance rejection. An informal alternate proof of the internal model principle in the state variable domain is presented using an operator-transformation technique. Where necessary, observers are used to complement the servo-controller. The proposed optimal robust servo-controller yields the expected superior performance in terms of response and error minimization. An illustrative example is given.