  The fundamental processes of absorption, stimulated and spontaneous emission,
and elastic as well as inelastic scattering involving light and atoms,
molecules, and nano-particles have been studied for decades using both
classical and quantum theories. While providing an overview of the subject,
this paper presents a streamlined approach to studying atom-photon interactions
in the context of modern quantum optics in the hope of providing guidance for
applications in the general area of molecular and nano-photonic machines.
