The form of quantom theory of radiation introduced by Heisenberg ig discussed from the point of view of the transformation theory of quantum electrodynamics. A general investigation of the connection between Heisenberg's method and Dirac's method of variation of parameters is given.The extension of Heisenberg's method to eigenvalue problems, which was first carried out by Weisskopf for the soIf energy of the electron, is presented in such a way as to show more clearly its quantum nehanical interpretation. A general proof of the equivalence of Weigkopf's method and the method of the perturbation theory of stationary States in quantum mechanics is given.