Galaxies are believed to become active by a process where two gas-rich galaxies merge, causing gas inflow to the supermassive black hole, which will then fuel the activity. As one of the most luminous types of active galaxies, quasars can be used for studying the growth of supermassive black holes in galaxies. The location of quasars in the large-scale structure of the universe can give us valuable information on the co-evolution of galaxies and the supermassive black holes. Our latest results on the environments of quasars suggest that both the local and large scale environments affect the evolution of activity in galaxies.