  While the total interior mass of a galaxy is reasonably well determined by a
good rotation curve, the relative contributions from disk, bulge and halo are
only weakly constrained by one-dimensional data. Barred galaxies are
intrinsically more complicated, but provide much tighter constraints on the
disk masses and support the idea that most of the mass in the inner parts of
bright galaxies is in their stars. There appears to be no systematic difference
in dark matter content between barred and unbarred galaxies, consistent with
the theoretical result that the global stability of galaxies with dense centers
does not depend on their halo fraction. The rotation curve shapes of lower
luminosity and low-surface-brightness galaxies, on the other hand, indicate
significant mass in the DM halo even near their centers. We find that most DM
halos appear to have large cores, inconsistent with the predictions from
cosmological simulations. We also show that such large-core halos can result
from compression by disk infall of physically reasonable initial halos. Maximum
disks, while apparently required by the data, do seem to present some puzzles;
most notably they re-open the old disk-halo ``conspiracy'' issue and
incorrectly predict that surface brightness should be a second parameter in the
Tully-Fisher relation.
