  We discuss the theory of electromagnetic fields, with an emphasis on aspects
relevant to radiofrequency systems in particle accelerators. We begin by
reviewing Maxwell's equations and their physical significance. We show that in
free space, there are solutions to Maxwell's equations representing the
propagation of electromagnetic fields as waves. We introduce electromagnetic
potentials, and show how they can be used to simplify the calculation of the
fields in the presence of sources. We derive Poynting's theorem, which leads to
expressions for the energy density and energy flux in an electromagnetic field.
We discuss the properties of electromagnetic waves in cavities, waveguides and
transmission lines.
