I am a Regents’ Professor of Astronomy in the Department of Astronomy and Steward Observatory, at the University of Arizona, USA. I am an extragalactic observational astronomer, mainly interested in the formation and evolution of galaxies, quasars, supermassive black holes and the intergalactic medium in the early universe. Our team has discovered most of the high-redshift quasars currently known at the epoch of cosmic reionization. These objects indicate a rapid growth of black holes in the early universe, and a strong connection between early black hole growth and the formation of the first massive galaxies. Meanwhile, observations Gunn- Peterson absorption in the quasar spectra directly map the history of reionization at the end of cosmic dark ages. My research has also been closely associated with large scale imaging and spectroscopic surveys, and with applying innovative techniques to these large datasets.