Book excerpt: This book describes the subject of electrodynamics at classical as well as quantum level, developed as an interaction at a distance. Thus it has electric charges interacting with one another directly and not through the medium of a field. In general such an interaction travels forward and backward in time symmetrically, thus apparently violating the principle of causality. It turns out, however, that in such a description the cosmological boundary conditions become very important. The theory therefore works only in a cosmology with the right boundary conditions; but when it does work it is free from the divergences that plague a quantum field theory.