Although the classical and quantum theories of Raman scattering of light by optical phonons have been well established, the papers genarally emphasized on some particular aspects of the scattering. For this reason, we need to develop a gene ral quantum theory of Raman scattering, taking account of both nonpolar and pola r modes. In our quantum theory, Raman scattering of light by longitudinal and tr ansverse polar modes can be described within a unified theoretical framework.