Abstract: Recently, the roadmap for nuclear fusion has been accepted and a new European consortium for the development of the science and technology for a nuclear fusion reactor has been set-up. In this lecture, it will be explained what fusion is, and we will how a fusion reactor should be designed. Then, I will give an overview of a few scientific and technological elements of the roadmap, with special emphasis on the development of:
-1- integrated scenarios with high fusion performance and plasma stability,
-2- solutions for the exhaust of heat and particles, and, if time allows
-3- the maintenance of ITER