Introduction and review of the year, including OP issues

In 2011, the LHC entered its phase of real luminosity production, with more than 5 fb - 1 delivered to the high luminosity experiments. All this was possible thanks to the continuous increase of machine performance and its good reliability, despite the many problems met during the year. A review of the major events is given, with a list of the issues met and all the steps that lead to a very successful year.