  Studies of planet migration derived from disc planet interactions began
before the discovery of exoplanets. The potential importance of migration for
determining orbital architectures being realised, the field received greater
attention soon after the initial discoveries of exoplanets. Early studies based
on very simple disc models indicated very fast migration times for low mass
planets that raised questions about its relevance. However, more recent
studies, made possible with improving resources, that considered improved
physics and disc models revealed processes that could halt or reverse this
migration. That in turn led to a focus on special regions in the disc where
migration could be halted. In this way the migration of low mass planets could
be reconciled with formation theories. In the case of giant planets which have
a nonlinear interaction with the disc, the migration should be slower and
coupled to the evolution of the disc. The latter needs to be considered more
fully to make future progress in all cases. Here we are primarily concerned
with processes where migration is connected with the presence of the
protopolanetary disk. Migration may also be induced by disc-free gravitational
interactions amongst planets or with binary companions. This is only briefly
discussed here.
