  This paper reviews the current state of our understanding of high-speed solar
wind acceleration in coronal holes. Observations by SOHO, coupled with
interplanetary particle measurements going back several decades, have put
strong constraints on possible explanations for how the protons, electrons, and
minor ions receive their extreme kinetic properties. The asymptotic plasma
conditions of the wind depend on energy and momentum deposition both at the
coronal base (where, e.g., the mass flux is determined) and in the extended
acceleration region between 2 and 10 solar radii (where the plasma becomes
collisionless and individual particle species begin to exhibit non-Maxwellian
velocity distributions with different moments). The dissipation of
magnetohydrodynamic fluctuations (i.e., waves, turbulence, and shocks) is
believed to dominate the heating in the extended corona, and spectroscopic
observations from the UVCS instrument on SOHO have helped to narrow the field
of possibilities for the precise modes, generation mechanisms, and damping
channels. We will survey recent theoretical and observational results that have
contributed to new insights, and we will also show how next-generation
instruments can be designed to identify and characterize the dominant physical
processes to an unprecedented degree.
