Cosmic Dawn: Studies of the Earliest Galaxies and Their Role in Cosmic
  Reionization
  I review recent progress and challenges in studies of the earliest galaxies,
seen when the Universe was less than 1 billion years old. Can they be used as
reliable tracers of the physics of cosmic reionization thereby complementing
other, more direct, probes of the evolving neutrality of the intergalactic
medium? Were star-forming galaxies the primary agent in the reionization
process and what are the future prospects for identifying the earliest systems
devoid of chemical enrichment? Ambitious future facilities are under
construction for exploring galaxies and the intergalactic medium in the
redshift range 6 to 20, corresponding to what we now consider the heart of the
reionization era. I review what we can infer about this period from current
observations and in the near-future with existing facilities, and conclude with
a list of key issues where future work is required.
