  Gamma-Ray Bursts (GRBs) are the most violent explosions in the Universe. Long
duration GRBs are associated with the collapse of massive stars, rivaling their
host galaxies in luminosity. The discovery of the most distant
spectroscopically confirmed object in the Universe, GRB090423, opened a new
window on the high redshift Universe, making it possible to study the cosmic
're-ionization' epoch and the preceding dark ages, as well as the generation of
the first stars (Population III) using GRBs. Obviously this enables a wealth of
new studies using the near infrared (nIR) characteristics of GRB afterglows.
Here we explore a different path, focusing on the next generation of X-ray
missions with large area focusing telescopes and fast repointing capabilities.
We found that X-ray data can complement nIR observations and for the brightest
GRBs can provide an accurate and independent redshift determination.
Metallicity studies can also be carried out profitably once the redshift is
known. Finally we discuss observational signatures of GRBs arising from
Population III stars in the X-ray band.
