Debris disks are faint disks surrounding main-sequence stars. Their occurrence at ages beyond the typical dissipation time scales of YSO disks suggests that they are secondary in nature, being refurbished by the collisions of bodies of not-so-well known sizes, hence the importance of the subject for our understanding of the evolution of planetary systems. IRAS has discovered debris disks, ISO and now especially Spitzer have substantially refined our understanding of them. With Herschel we will have a unique opportunity to study debris disks in the wavelength range where their SEDs peak, and with the spatial resolution needed to unravel their structure and composition.