Absorption spectroscopy of gamma-ray burst afterglows Probing the GRB line of sight

GRB absorption spectroscopy opened up a new window in the study of the high redshift Universe, especially with the launch of the Swift satellite and the quick and precise localization of the afterglow. Eight-meter class telescopes can be repointed within a few hours from the GRB, enabling the acquisition of high signal-to-noise ratio and high resolution afterglow spectra. In this paper I will give a short review of what we learned through this technique, and I will present some of the first results obtained with the X-shooter spectrograph.