[en] The Core Master 2 (CM2) system is the ABB state of the art tool for integrated on line and off line evaluation of the behaviour of BWR and PWR cores. The main features of CM2 are the advanced 3-D, 2-group neutronics of the Core Simulator, the integrated database and the graphical user interface, which makes CM2 the ideal calculation tool for engineering analysis of LWR cores. The Core Master 2 On-line System (CM2On) represents the new generation Core Monitoring Systems from ABB. CM2On performs evaluation of the status of the reactor core during operation, providing the reactor operator with thermal margins to licensed thermal limits. (author)