At the turn of the twenty-first century a golden era is occurring in observational cosmology. The new generation of large telescopes, combined with the capabilities of the Hubble Space Telescope and other space missions, allow astronomers to directly observe galaxy assembly over cosmic time. These developments demand a new generation of scientists trained in the methods suited to the study of distant galaxies. This timely volume contains the lectures delivered at the XI Canary Islands Winter School of Astrophysics, reviewing both scientific results and the main questions in the field. It covers the study of normal galaxies, distant galaxies, and studies based on far-infrared diagnostics, it reviews quasar absorption lines, and the properties of nearby galaxies. Each chapter is written by a world expert in the field, making the book an essential reference for all astronomers working in the field of high-redshift galaxies.