The spectacular development of new sources of electromagnetic radia-
radiation spanning the range of frequencies from rf to the far ultraviolet (lasers,
masers, synchrotron sources, etc.) has generated considerable interest in
the interaction processes between photons and atoms. New methods have
been developed, leading to a more precise understanding of the structure
and dynamics of atoms and molecules, to better control of their internal
and external degrees of freedom, and also to the realization of novel
radiation sources. This explains the growing interest in the low-energy
interaction between matter and radiation on the part of an increasing
number of researchers drawn from physics, chemistry, and engineering.
This work is designed to provide them with the necessary background to
understand this area of research, beginning with elementary quantum
theory and classical electrodynamics.