  In this article, we review the principles of macroscopic quantum
electrodynamics and discuss a variety of applications of this theory to
medium-assisted atom-field coupling and dispersion forces. The theory
generalises the standard mode expansion of the electromagnetic fields in free
space to allow for the presence of absorbing bodies. We show that macroscopic
quantum electrodynamics provides the link between isolated atomic systems and
magnetoelectric bodies, and serves as an important tool for the understanding
of surface-assisted atomic relaxation effects and the intimately connected
position-dependent energy shifts which give rise to Casimir-Polder and van der
Waals forces.
