  Magnetic fields are an important ingredient to cool star physics, and there
is great interest in measuring fields and their geometry in order to understand
stellar dynamos and their influence on star formation and stellar evolution.
During the last few years, a large number of magnetic field measurements became
available. Two main approaches are being followed to measure the Zeeman effect
in cool stars; 1) the measurement of polarized light, for example to produce
magnetic maps, and 2) the measurement of integrated Zeeman broadening to
measure the average magnetic field strength on the stellar surface. This
article briefly reviews the two methods and compares results between them that
are now available for about a dozen M-type stars. It seems that we see a great
variety of magnetic geometries and field strengths with typical average fields
of a few kG in active M-type stars. The interpretation of geometries, however,
has not yet led to a clear picture of magnetic dynamos and field configuration,
and work is needed on more observational data but also on the fundamental
understanding of our measurements.
