The Master Energy on energy choices for a carbon free future is carried by the 3 engineering schools of PSL: MINES ParisTech, Chimie ParisTech and ESPCI Paris. This training covers all the areas on which the transformation of the energy sector will be based. Good numbers of scenarios indicate that the sustainability of our ecosystem only makes sense if we are able to reduce CO2 emissions by 2050 by a factor of 4. Key areas are identified but the technologies to support this change are: for many of them at the development stage and there is still room for innovation at several scales: materials, components and energy systems.