The water-waves problem consists in finding the motion of the free surface of a perfect, incompressible and irrotational fluid under the influence of gravity. Such a motion is described by the Euler Equations with free surface. I will propose a proof of the well-posedness of these equations, which is quite elementary. I will comment on various of the tools involved in the proof: Dirichlet-to-Neuman operators, regularizing diffeomorphisms, shape optimization, Nash-Moser iterative scheme, etc.