  The weak coupling limit for a quantum system, with discrete energy spectrum,
coupled to a Bose reservoir with the most general linear interaction is
considered: under this limit we have a quantum noise processes substituting for
the field. We obtain a limiting evolution unitary on the system and noise space
which, when reduced to the system's degrees of freedom, provide the master and
Langevin equations that are postulated on heuristic grounds by physicists. In
addition we give a concrete application of our results by deriving the
evolution of an atomic system interacting with the electrodynamic field without
recourse to either rotating wave or dipole approximations.
