  Spiral galaxies host dynamically important magnetic fields which can affect
gas flows in the disks and halos. Total magnetic fields in spiral galaxies are
strongest (up to 30 \muG) in the spiral arms where they are mostly turbulent or
tangled. Polarized synchrotron emission shows that the resolved regular fields
are generally strongest in the interarm regions (up to 15 \muG). Faraday
rotation measures of radio polarization vectors in the disks of several spiral
galaxies reveal large-scale patterns which are signatures of coherent fields
generated by a mean-field dynamo. -- Magnetic fields are also observed in radio
halos around edge-on galaxies at heights of a few kpc above the disk.
Cosmic-ray driven galactic winds transport gas and magnetic fields from the
disk into the halo. The magnetic energy density is larger than the thermal
energy density, but smaller than the kinetic energy density of the outflow. The
orientation of field lines allows to estimate the wind speed and direction.
There is no observation yet of a halo with a large-scale coherent dynamo
pattern. A global wind outflow may prevent the operation of a dynamo in the
halo. -- Halo regions with high degrees of radio polarization at very large
distances from the disk are excellent tracers of interaction between galaxies
or ram pressure of the intergalactic medium. The observed extent of radio halos
is limited by energy losses of the cosmic-ray electrons. -- Future
low-frequency radio telescopes like LOFAR and the SKA will allow to trace halo
outflows and their interaction with the intergalactic medium to much larger
distances.
