This book presents extended forms of the Maxwell equations as well as electromagnetic fields, based on a non-zero divergence of the electric field and a non-zero electric conductivity in vacuo. These approaches, which predict new features of the electromagnetic field, such as the existence of both longitudinal and transverse solutions, the existence of displacement current in vacuo, and steady electromagnetic equilibria, have possible applications to charge-neutral leptons and new photon physics. The present theory can also clear up some unsolved problems, such as the total reflection of...