Extreme Light Infrastructure (ELI), the first research facility hosting an exawatt class laser will be built with a joint international effort and form an integrated infrastructure comprised at last three branches: Attosecond Science (in Szeged, Hungary) designed to make temporal investigation at the attosecond scale of electron dynamics in atoms, molecules, plasmas and solids. High Field Science will be mainly focused on producing ultra intense and ultra short sources of electons, protons and ions, coherent and high energetic X rays (in Prague, Czech Republic) as well as laserbased nuclear physics (in Magurele, Romania). The location of the fourth pillar devoted to Extreme Field Science, which will explore laser-matter interaction up to the non linear QED limit including the investigation of vacuum structure and pair creation, will be decided after 2012. The research activities will be based on an incremental development of the light sources starting from the current high intensity lasers (APOLLON, GEMINI, Vulcan and PFS) as prototypes to achieve unprecedented peak power performance, from tens of petawatt up to a fraction of exawatt (10 18 W). This last step will depend on the laser technology development in the above three sites as well as in current high intensity laser facilities.