  'Debris disks' are collections of small bodies around stars, such as the
Asteroid Belt and Kuiper Belt in our Solar System. These disks are composed of
objects smaller than planets, including asteroids, comets, dust, and dwarf
planets. We detect debris disks around a significant fraction of stars, and
these disks appear to be common components of planetary systems. Extrasolar
debris disks have a broad range of locations, shapes and features. This chapter
provides an introduction to debris disks around main-sequence stars. It
summarises our understanding of the field, and covers a wide range of concepts
from observations and theory. It describes how we detect extrasolar debris
disks, what we see, and what these observations tell us. It also describes how
debris disks evolve, and how they interact with planets. The chapter concludes
by discussing several unsolved questions in debris-disk science.
