  Stellar coronae, defined by the ensemble of magnetic field structures above
stellar photospheres and chromospheres together with their thermal or
non-thermal plasma content, play an important role in our understanding of
stellar magnetic fields, the stellar magnetic dynamo, and interactions between
a star and its environment. The most important wavelength regions from which we
have learned diagnostically on stellar coronae include the radio range and the
X-ray domain. The former is sensitive to accelerated electrons in magnetic
fields, and that has provided the only direct means of imaging stellar coronal
structure, through very long baseline interferometry. The soft X-ray diagnostic
power has been instrumental for our understanding of physical processes in the
hot, magnetically trapped coronal plasma, and the recent advent of
high-resolution X-ray spectroscopy is now accessing physical parameters of
coronal plasma directly. The adjacent extreme ultraviolet range contains
diagnostics relevant for the same temperature range as X-rays. The present
chapter provides a ``stellar astronomer's view'' of magnetic coronae,
summarizing basic physical processes relevant for our understanding of
radio/X-ray observations of coronal stars.
