  Galactic cosmic rays are believed to be accelerated at supernova remnant
shocks. Gamma-ray observations of both supernova remnants and associated
molecular clouds have been used in several occasions to test (so far quite
successfully) this popular hypothesis. Despite that, a conclusive solution to
the problem of cosmic ray origin is still missing, and further observational
and theoretical efforts are needed. In this paper, the current status of these
investigations is briefly reviewed.
