  The existing disk instability model for dwarf nova eruptions is reviewed, in
the light of recent progress in the understanding of angular momentum transport
in accretion disks. It is proposed that the standard lower branch in the
``S-curve'' in the effective temperature-surface density plane may not exist.
Rather, angular momentum transport may be suppressed in quiescence as a result
of cooling. The model for superoutbursts is also examined, and it is pointed
out that recent simulations strongly support the idea of a thermal-tidal
instability.
