  The energy range between about 100 keV and 1 GeV is of interest for a vast
class of astrophysical topics. In particular, (1) it is the missing ingredient
for understanding extreme processes in the multi-messenger era; (2) it allows
localizing cosmic-ray interactions with background material and radiation in
the Universe, and spotting the reprocessing of these particles; (3) last but
not least, gamma-ray emission lines trace the formation of elements in the
Galaxy and beyond. In addition, studying the still largely unexplored MeV
domain of astronomy would provide for a rich observatory science, including the
study of compact objects, solar- and Earth-science, as well as fundamental
physics. The technological development of silicon microstrip detectors makes it
possible now to detect MeV photons in space with high efficiency and low
background. During the last decade, a concept of detector ("ASTROGAM") has been
proposed to fulfil these goals, based on a silicon hodoscope, a 3D
position-sensitive calorimeter, and an anticoincidence detector. In this paper
we stress the importance of a medium size (M-class) space mission, dubbed
"ASTROMEV", to fulfil these objectives.
