  Cosmic rays (CRs) generate diffuse emission while interacting with the
Galactic magnetic field (B-field), the interstellar gas and the radiation
field. This diffuse emission extends from radio, microwaves, through X-rays, to
high-energy gamma rays. Diffuse emission has considerably increased the
interest of the astrophysical community due to recent detailed observations by
Planck, Fermi-LAT, and by very-high-energy Cherenkov telescopes. Observations
of this emission and comparison with detailed predictions are used to gain
information on the properties of CRs, such as their density, spectra,
distribution and propagation in the Galaxy. Unfortunately disentangling and
characterizing this diffuse emission strongly depends on uncertainties in the
knowledge of unresolved sources, gas, radiation fields, and B-fields, other
than CRs throughout the Galaxy. We report here on recent multiwavelength
observations of the Galactic diffuse emission, and discuss the diffuse emission
produced by CRs and its model uncertainties, comparing observations with
predictions. The importance for forthcoming telescopes, especially for the
Square Kilometre Array Telescope (SKA) and the Cherenkov Telescope Array (CTA),
and for future missions at MeV energies is also addressed.
