Abstract　 　　

Discoveries of luminous quasars at z>6 indicate the existence of billion solar mass black holes at the end of cosmic reionization, merely a few hundred million years after the big bang. This rapid growth of supermaissve black hole population in the early universe is surprising and poses challenges to the theory of black hole and galaxy formation. I will first describe measurements of accretion properties of the earliest quasars, then focus on new ALMA, HST and ground observations to study the star formation process in their host galaxies. In particular, I will highly exciting new ALMA observations that suggest strong evolution in the relation between the masses of black holes and their host galaxies (M-sigma relation). .