Conventional light scattering methods measure light scattered by spontaneously excited fluctuations and provide its power spectrum. Since modes are thermally excited, their phases are random and do not have any physical meaning. Different from the basic principle of these conventional methods, we recently proposed a new method of light scattering providing "complex" spectra instead of power spectra. We call this new method the "(phase-)coherent light scattering method." It is based on a new measurement principle: Coherent modes having phase information are generated resonantly by an optically induced scanning interference pattern. By a phase-sensitive detection of the light scattered by the optically generated coherent modes, complex resonance spectra of these modes can be measured. This principle is applicable to any modes in condensed matter, including thermal and concentration diffusion modes, rotational modes, propagating sound modes (longitudinal and transverse phonons), and surface modes (ripplons and Rayleigh waves). Here we present the basic principle of our new method and the theoretical background of polarized dynamic light scattering.