  Plasma in the Sun's hot corona expands into the heliosphere as a supersonic
and highly magnetized solar wind. This paper provides an overview of our
current understanding of how the corona is heated and how the solar wind is
accelerated. Recent models of magnetohydrodynamic turbulence have progressed to
the point of successfully predicting many observed properties of this complex,
multi-scale system. However, it is not clear whether the heating in open-field
regions comes mainly from the dissipation of turbulent fluctuations that are
launched from the solar surface, or whether the chaotic "magnetic carpet" in
the low corona energizes the system via magnetic reconnection. To help pin down
the physics, we also review some key observational results from ultraviolet
spectroscopy of the collisionless outer corona.
