Quasars as probes of cosmological reionization
  Quasars are the most luminous non-transient sources in the epoch of
cosmological reionization (i.e., which ended a billion years after the Big
Bang, corresponding to a redshift of z ~ 5), and are powerful probes of the
inter-galactic medium at that time. This review covers current efforts to
identify high-redshift quasars and how they have been used to constrain the
reionization history. This includes a full description of the various processes
by which neutral hydrogen atoms can absorb/scatter ultraviolet photons, and
which lead to the Gunn-Peterson effect, dark gap and dark pixel analyses,
quasar near zones and damping wing absorption. Finally, the future prospects
for using quasars as probes of reionization are described.
