The French CEA (Commissariat l'nergie Atomique) is currently building the LMJ (Laser MgaJoule), at the CEA Laboratory CESTA near Bordeaux. The LMJ is designed to deliver about 1.8 MJ of 0.35 0m light to targets for high energy density physics experiments. CEA has imposed an industrial policy by dividing the LMJ development and construction into a dozen major contracts. Each of these contracts supplies the hardware (e.g. Capacitor bank) and the associated control System. CEA is the project manager of the centralized supervisor and the communication protocols between the several subsystems. CEA is also responsible for the integration of the subsystems which is a major challenge. This presentation discusses the integration strategy. It is a three step process, each taking place in a different site: factory acceptance tests at the subsystem level, Integration tests of the whole control system on a dedicated 'Integration Platform', and finally on site tests from an 'integration control room' (which is different from the operation control). This paper will describe the necessary integration and simulation tools and the tasks related to the three steps.