The solar corona, the outer atmosphere of the Sun, is heated to millions
of degrees. This is several orders of magnitude hotter than the
photosphere, the optical surface of the Sun, below, and a mystery that
has baffled scientists for centuries. The answer to the question of how
the solar corona is heated lies in the crucial magnetic connection
through the atmosphere of the Sun. The magnetic field that threads the
corona extends below the solar photosphere, where the convective motions
drag the magnetic field footpoints, tangling and twisting them. The
chromosphere is the atmospheric layer above the photosphere, below the
corona, and the magnetic field provides an important connection between
these layers. The exchange of mass and energy between the chromosphere
and corona is an essential piece of this puzzle. The connection between
the chromosphere and the corona is a challenging piece of the puzzle
both observationally and computationally, as it is highly complex in
space and time. We describe the history of the observations and
theoretical understanding of the heating of the solar atmosphere, and
end with future prospects of the coronal heating problem.