The Kuiper belt is a ring of icy planetesimals, i.e. comets, beyond the orbit of Neptune, a remnant of the formation of the solar system. These volatile-rich bodies never accreted into a planet because of the decreasing surface density of the solar nebula accretion disk and the increasingly long orbital periods at large heliocentric distances. The inner region of the Kuiper belt, between 34 and 45 AU, is dynamically active with an estimated population of ~6 times 10^9 objects, and it is likely the source of the Jupiter-family short-period comets. The dynamically inactive region beyond 45 AU may extend out to 10^3 AU or more and may contain up to several times 10^13 objects with a total mass of several hundred Earth masses. Observational searches have so far discovered 18 objects in the Kuiper belt, ranging in diameter from ~90 to 350 km. IRAS dust disks around nearby stars are likely similar, comet belt structures.