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M31 and M33 impress by their enormous angular extent on sky. Even single-dish radio telescopes with low angular resolution reveal many details. M31 was the first spiral galaxy to be detected in radio continuum 50 years ago (just a few months before I was born) and the favourite galaxy for the Effelsberg 100-m telescope (see Wielebinski, this volume). The ring-like structure seen in most spectral ranges (except in the optical, unfortunately) gives M31 its beauty. The radio ring of M31 (Fig. 1) was elected worth to be displayed on a stamp of the German postal services in 1999 as an example of "fascinating phenomena in the Cosmos" (see back cover).