The TiO2-based DeNOx catalyst which is now commercially implemented world-wide is described, emphasizing the importance of the resistance to SOx-poisoning and plugging by particulates. Various NOx reduction technologies are compared and recent trends in catalytic DeNOx installations in Japan are reviewed. For wider applications and to meet the stringent emission requirements, newly developed DeNOx catalysts such as for high-temperature gas turbine exhaust and for simultaneous removal of NOx and CO are also introduced.