  The physical ingredients to describe the epoch of cosmological recombination
are amazingly simple and well-understood. This fact allows us to take into
account a very large variety of processes, still finding potentially measurable
consequences. In this contribution we highlight some of the detailed physics
that were recently studied in connection with cosmological hydrogen and helium
recombination. The impact of these considerations is two-fold: (i) the
associated release of photons during this epoch leads to interesting and unique
deviations of the Cosmic Microwave Background (CMB) energy spectrum from a
perfect blackbody, which, in particular at decimeter wavelength, may become
observable in the near future. Despite the fact that the abundance of helium is
rather small, it also contributes a sizeable amount of photons to the full
recombination spectrum, which, because of differences in the dynamics of the
helium recombinations and the non-trivial superposition of all components, lead
to additional distinct spectral features. Observing the spectral distortions
from the epochs of hydrogen and helium recombination, in principle would
provide an additional way to determine some of the key parameters of the
Universe (e.g. the specific entropy, the CMB monopole temperature and the
pre-stellar abundance of helium), not suffering from limitations set by cosmic
variance. Also it permits us to confront our detailed understanding of the
recombination process with direct observational evidence. (ii) with the advent
of high precision CMB data, e.g. as will be available using the Planck Surveyor
or CMBpol, a very accurate theoretical understanding of the ionization history
of the Universe becomes necessary for the interpretation of the CMB temperature
and polarization anisotropies. (abridged)
