  The X-ray emission from the Sun reveals a very dynamic hot atmosphere, the
corona, which is characterized by a complex morphology and broad range of
timescales of variability and spatial structuring. The solar magnetic fields
play a fundamental role in the heating and structuring of the solar corona.
Increasingly higher quality X-ray solar observations with high spatial (down to
subarcsec) and temporal resolution provide fundamental information to refine
our understanding of the solar magnetic activity and of the underlying physical
processes leading to the heating of the solar outer atmosphere. Here we provide
a brief historical overview of X-ray solar observations and we summarize recent
progress in our understanding of the solar corona as made possible by
state-of-the-art current X-ray observations.
