  After a short introduction on how we get information of the magnetic fields
from radio observations I discuss the results concerning the magnetic field
structure in galaxies: Large-scale regular magnetic field pattern of spiral
structure exist in grand-design spirals, flocculent and even irregular
galaxies. The regular field in spirals is aligned along the optical spiral arms
but strongest in the interarm region, sometimes forming 'magnetic arms'. The
strongest total field is found in the optical arms, but mainly irregular. The
large-scale regular field is best explained by some kind of dynamo action. Only
a few galaxies show a dominant axisymmetric field pattern, most field
structures seem to be a superposition of different dynamo modes or rather
reveal more local effects related to density waves, bars or shocks.
Observations of edge-on galaxies show that the magnetic fields are mainly
parallel to the disk except in some galaxies with strong star formation and
strong galactic winds as e.g. NGC 4631.
