Abstract: Output regulation is to control the output of a system so as to achieve asymptotical tracking of prescribed trajectories or asymptotical rejection of disturbances. For linear systems the internal model principle is a powerful tool to solve this problem. In the last decade the problem of the output regulation and the internal model principle of nonlinear systems have become a frontier of the international nonlinear control researches. The purpose of this paper is to give a survey on this problem.