  We summarize evidence that the halo of the Milky Way comprises two different,
and broadly overlapping, stellar components. The two structures exhibit
different chemical compositions, spatial distributions, and kinematics. These
results were obtained through an analysis of more than 20,000 calibration stars
from the Sloan Digital Sky Survey (SDSS). The duality of the stellar halo
directly impacts galaxy formation models, for the Milky Way and other large
spirals.
