  Planet-disk interactions, where an embedded massive body interacts
gravitationally with the protoplanetary disk it was formed in, can play an
important role in reshaping both the disk and the orbit of the planet. Spiral
density waves are launched into the disk by the planet, which, if they are
strong enough, can lead to the formation of a gap. Both effects are observable
with current instruments. The back-reaction of perturbations induced in the
disk, both wave-like and non-wavelike, is a change in orbital elements of the
planet. The efficiency of orbital migration is a long-standing problem in
planet formation theory. We discuss recent progress in planet-disk interactions
for different planet masses and disk parameters, in particular the level of
turbulence, and progress in modeling observational signatures of embedded
planets.
