  Diffuse emission from the Milky Way dominates the gamma-ray sky. About 80% of
the high-energy luminosity of the Milky Way comes from processes in the
interstellar medium. The Galactic diffuse emission traces interactions of
energetic particles, primarily protons and electrons, with the interstellar gas
and radiation field, thus delivering information about cosmic-ray spectra and
interstellar mass in distant locations. Additionally, the Galactic diffuse
emission is the celestial foreground for the study of gamma-ray point sources
and the extragalactic diffuse gamma-ray emission. We report on the latest
developments in the modelling of the Galactic diffuse emission, which will be
used for the Gamma Ray Large Area Space Telescope (GLAST) investigations.
