In this talk we briefly survey several mechanisms for scattering photons in the early Universe and how these mechanisms may reveal themselves. We will first discuss the impact of Rayleigh scattering of CMB photons on photon and baryon observables from the early Universe. We then discuss the scattering of photons in the 21-cm "spin-flip" line of neutral hydrogen and how these scatterings can result in cosmic 21-cm fluctuations from the cosmic dark ages. These high-redshift 21-cm fluctuations, should they be observable, would provide a three dimensional picture of the dark-age Universe and an unprecedented amount of cosmological information.
Finally, if time permits, we will discuss a particle physics model where photons are resonantly scattered by dark matter and the observational signatures of such a scenario.