On the basis of the spatial distribution, intensity, and energy spectrum, the diffuse Galactic high-energy gamma radiation is believed to be the result of cosmic-ray interactions with matter, and to a lesser extent photons. This paper describes a model calculation of diffuse gamma-ray emission based on these interactions. Recent radio observations of the main interstellar components of matter on a scale of 0.°5 are used for the entire region within 10° of the Galactic plane. A three-dimensional spatial model of the Galaxy is used to compute the emission from each volume element based on the matter, cosmic ray, and photon densities using well know interaction processes