  The dust disks observed around mature stars are evidence that plantesimals
are present in these systems on spatial scales that are similar to that of the
asteroids and the KBOs in the Solar System. These dust disks (a.k.a. ``debris
disks'') present a wide range of sizes, morphologies and properties. It is
inferred that their dust mass declines with time as the dust-producing
planetesimals get depleted, and that this decline can be punctuated by large
spikes that are produced as a result of individual collisional events. The lack
of solid state features indicate that, generally, the dust in these disks have
sizes larger than approximately 10 microns, but exceptionally, strong silicate
features in some disks suggest the presence of large quantities of small
grains, thought to be the result of recent collisions. Spatially resolved
observations of debris disks show a diversity of structural features, such as
inner cavities, warps, offsets, brightness asymmetries, spirals, rings and
clumps. There is growing evidence that, in some cases, these structures are the
result of the dynamical perturbations of a massive planet. Our Solar System
also harbors a debris disk and some of its properties resemble those of
extra-solar debris disks. From the cratering record, we can infer that its dust
mass has decayed with time, and that there was at least one major ``spike'' in
the past during the Late Heavy Bombardment. This offers a unique opportunity to
use extra-solar debris disks to shed some light in how the Solar System might
have looked in the past. Similarly, our knowledge of the Solar System is
influencing our understanding of the types of processes which might be at play
in the extra-solar debris disks.
