The diffuse γ-ray emission originated in the Galaxy is the main contributor to the photons ob- served by the Fermi-Large Area Telescope. It is a foreground or a background for the deter- mination and the understanding of point sources and of diffuse processes. The diffuse galactic γ-ray emission is produced by the interactions of cosmic ray nuclei on the interstellar gas and of electrons on the interstellar radiation field. We discuss the impact that the charged cosmic rays (CRs) have on the determination of the gamma-ray diffuse galactic emission. We review the implications deriving from present data and outline some future prospects for data and models.