The classical particle interactions based on a covariant action principle directly lead, after path integration to the perturbation expansion of
QED and to Feynman graphs without the intermediary of quantized fields Both scalar electrodynamics and spinor electrodynamics are treated The
latter is based on a covariant classical model of the Dirac electron which already provides the notion of antiparticles and zitterbewegung so that
vacuum polarization and pair production can also be discussed We give a procedure on how classical spin leads to quantum spin in successive
time-sliced integrations