  As the likely birthplaces of planets and an essential conduit for the buildup
of stellar masses, inner disks are of fundamental interest in star and planet
formation. Studies of the gaseous component of inner disks are of interest
because of their ability to probe the dynamics, physical and chemical
structure, and gas content of this region. We review the observational and
theoretical developments in this field, highlighting the potential of such
studies to, e.g., measure inner disk truncation radii, probe the nature of the
disk accretion process, and chart the evolution in the gas content of disks.
Measurements of this kind have the potential to provide unique insights on the
physical processes governing star and planet formation.
