[en] In this discussion of photon scattering from atoms, we distinguish between elastic and inelastic scattering, and we restrict our attention to the scattering of one photon from an isolated atom. We do not consider the absorption of that photon (atomic photoeffect), or multi-photon processes (as in an intense laser beam), or processes in which additional particles are created (as in photon splitting or creation of electron-positron pairs), or effects of atomic environments (as in solids or plasmas). We also do not consider two-step processes involving substantial time delays, which can be understood in terms of absorption and subsequent re-emission (fluorescence)