We discuss some of the main open issues in the evolution of Active Galactic
Nuclei which can be solved by the sensitive, wide area surveys to be performed
by the proposed Wide Field X-ray Telescope mission.Comment: Proceedings of "The Wide Field X-ray Telescope Workshop", held in
Bologna, Italy, Nov. 25-26 2009. To appear in Memorie della Societa'
Astronomica Italiana 2010 (arXiv:1010.5889