Abstract: The concept of harmonic control between two systems is presented. Necessary and sufficient conditions are given for harmonical stabilization of two systems. These results can be generalized to harmonic stability problems for more than two systems. Examples are given to illustrate the results. The results in this paper show that two systems can be easily harmonically stabilized under self-feedback and interconnected feedback. It is possible for the control framework given here to play a useful role in the stabilization of composite systems.