Using a very general formulation of the Internal Model Principle for infinite-dimensional systems it is shown that a robust controller tracking/rejecting signals generated by an infinite-dimensional exosystem can be decomposed into a servocompensator and a stabilizing controller. The servocompensator contains an internal model of the exosystem generating the reference and disturbance signals and the stabilizing controller stabilizes the infinite-dimensional closed-loop system. As such the decomposition gives a parametrization of robustly regulating controllers in the time domain. Various ways of stabilizing the closed-loop system are presented.