  We investigate the build-up of the accreted stellar and dark matter haloes of
Milky Way-like galaxies in APOSTLE suite of cosmological hydrodynamics
simulations. We show that the stellar halo is made up primarily of stars
stripped from a small number of massive dwarfs, most of which are disrupted by
the present day. The dark matter halo, on the other hand, is made up primarily
of small unresolved subhaloes ($\lesssim 10^6$ M$_{\odot}$) and a ``smooth''
component consisting of particles which were never bound to a subhalo. Despite
these differences, the massive dwarfs that make up the majority of the stellar
halo also contribute a significant fraction of the dark matter. The stars and
dark matter stripped from these dwarfs are related through their kinematics and
this leaves imprints in the phase-space structure of the haloes. We examine the
relation between the location of features, such as caustics, in the phase space
of the stars and dark halo properties. We show that the ``edge'' of the stellar
halo is a probe of dark matter halo mass and assembly history. The edges of
Milky Way-mass galaxies should be visible at a surface brightness of 31-36 mag
arcsec$^{-2}$.
