  Strong surface magnetic fields are ubiquitously found in M-dwarfs with mean
intensities on the order of few thousand Gauss-three orders of magnitude higher
than the mean surface magnetic field of the Sun. These fields and their
interaction with photospheric convection are the main source of stellar
activity, which is of big interest to study links between parent stars and
their planets. Moreover, the understanding of stellar magnetism, as well as the
role of different dynamo-actions in particular, is impossible without
explaining magnetic fields in M-dwarfs. Measuring magnetic field intensities
and geometries in such cool objects, however, is strongly limited to our
ability to simulate the Zeeman effect in molecular lines. In this work, we
present quantitative results of modelling and analysis of the magnetic fields
in selected M-dwarfs in FeH Wing-Ford lines and strong atomic lines. Some
particular FeH lines are found to be the excellent probes of the magnetic
field.
