This book explains why there are different variants of Maxwell's equations and the physical meaning of the quantities they contain. It also shows how the equations for static electric and magnetic potentials are derived from Maxwell's equations. Matter exposed to the field is an integral part of the discussion. Multipole developments are justified and derived. Furthermore, the potential for simplification in formulating dynamical theory as gauge field theory is explained. The laws of optics are derived from those of electrodynamics. Justifications are provided for quasi-stationary calculations, limits are formulated, and technical counterexamples are shown.