  Expectation values of the electromagnetic field and the electric current are
introduced at space-time resolution which belongs to the quantum domain. These
allow us to approach some key features of classical electrodynamics from the
underlying QED. One is the emergence of the radiation field in the retarded
solution of the Maxwell equation, derived from an action principle. Another
question discussed is the systematic derivation of the polarizability of a
charge system. Furthermore, the decoherence and the consistency of the photon
field is established by a perturbative calculation of the reduced density
matrix for the electromagnetic field within the Closed Time Path formalism.
