Since their first discovery about 60 years ago, quasars have been at the forefront of our understanding of the distant universe. We now know >400 quasars at redshift z>6, when the Universe was < 1 Gyr old. Their mere presence poses a challenge to models of the formation and early growth not only of their massive black holes, but also of their host galaxies, their dust content, and the large-scale structures where they reside. In the last few years, however, we have witnessed transformational leaps in our understanding of the properties of early quasars, thanks to unprecedented observational achievements, in particular with ALMA and JWST. We have now accurate black hole mass estimates in quasars up to z~7.6; we have mapped the gas and dust distribution in the quasar host galaxies down to 100 pc resolution, and quantified their star formation rate, metallicity, and other properties (gas density, photoionization conditions, etc); and we have secured a census of tens of spectroscopically-confirmed galaxies in the environment of quasars at z>6. These observational results allow us to sketch a novel picture on the formation of some of the most massive astrophysical sources in the early Universe. Those unable to attend the colloquium in person are invited to participate online through Zoom (Meeting ID: 942 0262 2849, passcode 792771) using the link: https://eu02web.zoom-x.de/j/94202622849?pwd=dGlPQXBiUytzY1M2UE5oUDRhbzNOZz09 Dr Decarli is available for meetings by arrangement with his host, Kathryn Kreckel (kathryn.kreckel@uni-heidelberg.de)