  Cavity quantum electrodynamics (CQED) investigates the interaction between
light confined in a resonator and particles, such as atoms. In recent years,
CQED experiments have reached the optical domain resulting in many interesting
applications in the realm of quantum information processing. For many of these
application it is necessary to overcome limitations imposed by photon loss. In
this context whispering-gallery mode (WGM) resonators have obtained significant
interest. Besides their small mode volume and their ultra high quality, they
also exhibit favorable polarization properties that give rise to chiral
light--matter interaction. In this chapter, we will discuss the origin and the
consequences of these chiral features and we review recent achievements in this
area.
