Refractive index of the intracavity medium can change with time in the case of dynamic optical resonators. Recently a novel phenomenon known as “adiabatic wavelength conversion” has been discovered in such resonators. We have developed a general theory of light propagation inside dynamic optical resonators using time-dependent perturbation theory of quantum mechanics. In this talk, I present this theory and discuss how it can used to understand the observed behavior of several recent experiments. Dynamic wavelength shifts can also occur in the absence of optical feedback. This situation will be discussed briefly using a novel time-transformation approach.