Quasar Absorption Lines

The absorption lines observed in quasar spectra have given us a detailed picture of the intergalactic medium and the metal abundance and kinematics of high redshift galaxies. In this review, we present an introduction to the field, starting with the techniques used for interpreting absorption line spectra. We then survey the observational and theoretical development of our understanding of the Lyman-alpha forest, the metal absorbers, and the damped Ly-alpha absorbers. We conclude with a discussion of some of the remaining outstanding issues, and prospects for the future.