Some contributions in Chap. 1 have highlighted the impact of the discovery in the 1960s of a handful of radio galaxies and Quasars in the redshift range z ∼ 0.2-0.4. About 40 years later, at the end of the twentieth Century, the systematic exploration of galaxies reached z ∼ 1-3. The combination of HST deep imaging and the coming into operation of the 8-10 m class telescopes with their spectroscopic capabilities, move ahead the limits. At the same time, astronomers greatly improved their strategies to hunt high-redshift galaxies. Today, it is not infrequent the spectroscopic confirmation of galaxies at z ∼ 7-8, pushing the detection limits more or less to the end of the re-ionization era. The gauntlet to observe the so called "first galaxies", i.e. those assembling during the first billion years of the cosmic time, is throw down.