  The bulk of the hydrogen in the universe transformed from neutral to ionized
somewhere in the redshift interval 5 < z < 40, most likely due to ionizing
photons produced by an early generation of stars or mini-quasars. The resulting
free electrons, interacting with the CMB photons via Thomson scattering, are a
mixed blessing, providing both a probe of the epoch of the first stars and a
contaminant to the pristine primary anisotropy. Here we review our current
knowledge of reionization with emphasis on inhomogeneities and describe the
possible connections to CMB anisotropy.
