Cosmic Magnetic Fields: What we know, what we must discover

Cosmic magnetic fields have now been studied for over 100 years. Although the initial detection was done at optical wavelengths, it was radio astronomy that gave us the bulk of information on cosmic magnetic fields in the recent years. In this review the observational results obtained by radio astronomy methods will be discussed. In particular maps of Galactic magnetic fields as well as magnetic fields in nearby galaxies will be presented. A discussion of possible developments in the near future will conclude this review.