  Galactic diffuse continuum gamma-ray emission is intricately related to
cosmic-ray physics and radio astronomy. We describe recent results from an
approach which endeavours to take advantage of this. Information from
cosmic-ray composition constrains the propagation of cosmic rays; this in turn
can be used as input for gamma-ray models. The GeV gamma-ray excess cannot be
explained as neutral pion decay resulting from a hard nucleon spectrum without
violating antiproton and positron data; the best explanation at present appears
to be inverse-Compton emission from a hard interstellar electron spectrum. One
consequence is an increased importance of Galactic inverse Compton for
estimates of the extragalactic background. At low energies, an additional
point-source component of gamma-rays seems to be necessary.
