Quasars at z>6 (when the universe is <1 Gyr old) are arguably the most active objects in the early universe. The high luminosity of a quasar is powered by rapid accretion of gas (>10 Msun/yr) on a central black hole with mass >1E8 Msun. Their host galaxies are forming stars at humongous rates (100-1000 Msun/yr). Copious reservoirs of gas sustain both star formation and nuclear accretion. The very presence of such compact concentrations of matter suggests that high-z quasars reside in the extreme peaks of the cosmic density distribution, so quasars could be used to pin-point the first galactic overdensities. These extreme properties make quasars unique laboratories of the birth and early formation of black holes and massive galaxies. I will present our on-going efforts aimed at discovering and characterizing new z>6 quasars, and at studying their host galaxies and their environment.