Amazing times! I finished the manuscript for the first edition of this book just 8 years
ago—but the necessity of a new edition was urgently felt. In these years we have witnessed
an enormous development in the field of extragalactic astronomy and cosmology. On the
instrument side, the ?nal servicing mission to the Hubble Space Telescope brought two
new very powerful instruments to this unique observatory, the Herschel and Planck satellites
were launched and conducted their very successful missions, the South Pole Telescope and
the Atacama Cosmology Telescope started operation, ALMA was inaugurated and began
observations, and new powerful high-resolution instruments were installed on 10-m class
telescopes. Scientifically, the redshift frontier has been extended, with candidate galaxies at
redshifts of ten or higher and stellar explosions seen at redshifts beyond eight, a much improved
understanding of the high-redshift galaxy population has been obtained, as a consequence
of which also the origin of the cosmic infrared background is now understood, and greatly
improved multi-wavelength surveys carried out with the most powerful telescopes, together
with new simulation techniques, have provided us with a much better understanding of the
evolution of the galaxy population. The Pierre Auger observatory has shed much light on
the origin of the most energetic cosmic rays, and the advances of atmospheric Cherenkov
telescopes have identified dozens of active galaxies emitting at energies of teraelectron Volts.