  Thousands of confirmed and candidate exoplanets have been identified in
recent years. Consequently, theoretical research on the formation and dynamical
evolution of planetary systems has seen a boost, and the processes of
planet-planet scattering, secular evolution, and interaction between planets
and gas/debris disks have been well-studied. Almost all of this work has
focused on the formation and evolution of isolated planetary systems, and
neglect the effect of external influences, such as the gravitational
interaction with neighbouring stars. Most stars, however, form in clustered
environments that either quickly disperse, or evolve into open clusters. Under
these conditions, young planetary systems experience frequent close encounters
with other stars, at least during the first 1-10 Myr, which affects planets
orbiting at any period range, as well as their debris structures.
