Atomic and Molecular Phases of the Interstellar Medium
  This review covers four current questions in the behavior of the atomic and
molecular interstellar medium. These include whether the atomic gas originates
primarily in cold streams or hot flows onto galaxies; what the filling factor
of cold gas actually is in galactic regions observationally determined to be
completely molecular; whether molecular hydrogen determines or merely traces
star formation; and whether gravity or turbulence drives the dynamical motions
observed in interstellar clouds, with implications on their star formation
properties.
