  We study quantum electrodynamics (QED) in the light-front dynamical form by
using null-plane causal perturbation theory. We establish the equivalence with
instant dynamics for the scattering processes, whose normalization allows to
construct the instantaneous terms of the usual null-plane QED Lagrangian
density. Then we study vacuum polarization and normalize it by studying its
insertions into M{\o}ller's scattering process, obtaining the complete photon's
propagator, which turns to be equivalent to the one of instant dynamics only
when gauge invariance is taken into account.
