  Techniques for inferring the radial and geometric form of dark matter halos
and the results they have produced to date are reviewed. Dark halos appear to
extend to at least ~50 kpc with total enclosed masses that rise linearly with
radius R. Whether this behavior can be extrapolated to distances as large as
200 kpc and beyond is controversial; results at this radius are
model-dependent. Observationally, the geometrical form of the dark halo can be
characterized by the equatorial axis ratio b/a (ovalness) and
vertical-to-equatorial axis ratio c/a (flattening) of the total density.
Different techniques consistently yield b/a > 0.7 (and thus b/a > 0.9 for the
potential) at R~20 kpc, with more axisymmetric values, b/a >~ 0.8, being more
likely. Results are less consistent for the vertical flattening, perhaps due to
the difference in the spatial regions probed by different techniques or
inappropriate assumptions. Techniques that probe furthest from the stellar
plane z~15 kpc consistently implicate substantially flattened c/a = 0.5 +/- 0.2
dark halos. These axis ratios are in acceptable agreement with expectations
from N-body simulations of cold dark matter mixed with ~10% dissipational gas.
