Photometric redshifts: spectroscopy AT Δλ / λ ≈ 0.1

I discuss the advantages that photometric redshift techniques offer over traditional (spectroscopic) redshift determination methods. It is shown that the former represents the only means we have of studying the faint distant galaxy population as a whole, and that, in its range of applicability, it delivers excellent results that can add to our knowledge of galaxy formation and evolution processes. Along this line, I also present some of the results extracted from a photometric redshift catalogue of galaxies in the Hubble Deep Field (HDF), including measurements of the star formation density in the high-redshift Universe, morphological evolution of galaxies, and detection of some of the most distant galaxies ever observed. This revised version was published online in July 2006 with corrections to the Cover Date.