  We describe a general multiplier method to obtain boundary stabilization of
the wave equation by means of a (linear or quasi-linear) Neumann feedback. This
also enables us to get Dirichlet boundary control of the wave equation. This
method leads to new geometrical cases concerning the "active" part of the
boundary where the feedback (or control) is applied. Due to mixed boundary
conditions, the Neumann feedback case generate singularities. Under a simple
geometrical condition concerning the orientation of the boundary, we obtain a
stabilization result in linear or quasi-linear cases.
