  We develop a simple theoretical framework for transport in magnetic
multilayers, based on Landauer-Buttiker scattering formalism and Random Matrix
Theory. A simple transformation allows one to go from the scattering point of
view to theories expressed in terms of local currents and electrochemical
potential. In particular, our theory can be mapped onto the well established
classical Valet Fert theory for collinear systems. For non collinear systems,
in the absence of spin-flip scattering, our theory can be mapped onto the
generalized circuit theory. We apply our theory to the angular dependance of
spin accumulation and spin torque in non-collinear spin valves.
