  Gamma-ray line observations provide a versatile tool for studies of
nucleosynthesis processes and supernova physics. In particular, the observation
of radioactive species in the interstellar medium probes recent nucleosynthesis
activity on various time-scales for different kinds of sources. Considerable
progress in gamma-ray instrumentation during the last decades has led to the
discovery of several cosmic gamma-ray lines. The best studied of these lines is
today the 1.809 MeV line attributed to the decay of radioactive 26Al within the
interstellar medium. In this review, recent observational results are presented
and their astrophysical implications are discussed.
