  Planetary magnetic fields are important indicators of planetary processes and
evolution, from a planet's outer core to its surface (if it possesses one) to
its atmosphere and near-space environment. Magnetic fields are most directly
measured in situ, and determining whether distant planetary objects possess
magnetic fields can be challenging. At present we have no unambiguous
measurements of magnetic fields on exoplanets. Nevertheless, it would be
surprising if at least some exoplanets did not generate a magnetic field, like
many planetary bodies in the solar system. This chapter provides an overview of
the current understanding of exoplanetary magnetic fields and their
consequences. In the next section we review the current understanding of
planetary dynamo generation as it applies to solar system objects and discuss
the implications for exoplanetary magnetic field generation. Following this, we
describe seven methods for determining the existence and strength of an
exoplanetary magnetic field and discuss the near-term prospects for each
method. We close by highlighting four main consequences of exoplanetary
magnetic fields for a planet and its evolution.
