26Al sources in the Galaxy as seen in the 1.809 MeV gamma-ray line

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.