  The annihilation of positrons in the Milky Way galaxy has been observed for
$\sim 50$ years however the production sites of these positrons remains hard to
identify. The observed morphology of positron annihilation gamma-rays provides
information on the annihilation sites of these Galactic positrons. It is
understood that the positrons responsible for the annihilation signal originate
at MeV energies. The majority of sources of MeV positrons occupy the thin, star
forming disk of the Milky Way. If positrons propagate far from their sources,
we must develop accurate models of positron propagation through all ISM phases
in order to reveal the currently uncertain origin of these Galactic positrons.
On the other hand, if positrons annihilate close to their sources, an
alternative source of MeV positrons with a distribution that matches the
annihilation morphology must be identified. In this work, I discuss the various
models that have been developed to understand the origin of the
$511\,\mathrm{keV}$ line from the direction of the Galactic bulge, and the
propagation of positrons in the ISM.
