  Our understanding of the structure and properties of accretion disks in
quiescent Dwarf Novae and X-ray Transients is very limited. Observations during
quiescence challenge some of the standard Disk Instability Model (DIM)
predictions. Our ignorance of the nature of viscosity may be the main source of
uncertainties in quiescent disk models. A ``layered accretion'' alternative to
the DIM, in which accretion proceeds via X-ray ionized surface layers,
illustrates the magnitude of these uncertainties. A detection of molecular
hydrogen in quiescent disks may provide direct constraints on the nature of
viscosity.
