  A review is given of recent theoretical work on the superfluid dynamics of
trapped Bose gases at finite temperatures, where there is a significant
fraction of non-condensate atoms. One can now reach large enough densities and
collision cross-sections needed to probe the collective modes in the
collision-dominated hydrodynamic region where the gas exhibits characteristic
superfluid behavior involving the relative motions of the condensate and
non-condensate components. The precise analogue of the Landau-Khalatnikov
two-fluid hydrodynamic equations was recently derived from trapped Bose gases,
starting from a generalized Gross-Pitaevskii equation for the condensate
macroscopic wavefunction and a kinetic equation for the non-condensate atoms.
