We identify the scientific prospects for studying low-energy cosmic rays, the interstellar medium, and the associated gamma-ray emissions with a next-generation wide-field telescope from 200 keV to ~10 GeV. With improved angular resolution and more than an order of magnitude better sensitivity than previous instruments, the All-sky Medium Energy Gamma-ray Observatory (AMEGO) would allow for the first time to study in detail the low-energy cosmic rays, which play a fundamental role in the formation of stars and in the dynamics of the interstellar medium. It would allow mapping the cosmic-ray distribution in order to understand their propagation in the Galaxy.
We discuss the importance of having such a telescope, and we present the predictions for the gamma-ray continuum both at large scale and in individual clouds, and for de-excitation nuclear lines.

This paper is based on the Astro2020: Decadal Survey on Astronomy and Astrophysics, science white papers, no. 151; Orlando E. et al. Bulletin of the American Astronomical Society, Vol. 51, Issue 3, id. 151 (2019) ‘Cosmic Rays and Interstellar Medium with Gamma-Ray Observations at MeV Energies’, where more details can be found.