  If the Galaxy formed hierarchically through the accretion of smaller
satellite galaxies we might hope to find signatures of this in the halo's
phase-space distribution. I review theoretical ideas about what form these
signatures should take, concentrating in particular on the characteristics of
debris from the tidal disruption of satellites less than the size of the Large
Magellanic Clouds and at distances greater than 10 kpc. Under these
circumstances, tidal debris can remain aligned in streams of stars close to the
satellite's original orbit for the lifetime of the Galaxy and we can understand
the evolution of its structure analytically. This understanding has many
applications to observations and I will discuss a few examples: reconstructing
the properties of a long-dead satellite from its debris; measuring the mass
loss rate from Galactic satellites through the density of extra-tidal stars;
and using observations of motions of tidal stream stars to measure the mass and
size of the Milky Way.
