Many gas-rich circumstellar disks are known around ``classical'' T Tauri stars (ctts), where strong H&alpha emission lines indicate viscous accretion onto the star. Approximately 50-70% of all ctts have disks with typical (gas + dust) masses of 10^-3 - 10^-1 times that of the Sun, sufficient to form a planetary system like our own.

Much less is known about later stages, when most of the gas may have disappeared and accretion has terminated. Non-accreting, tenuous dust disks were detected by IRAS and ISO around a handful of nearby A-type stars. Some have also been detected around nearby wTTs identified by ROSAT (Brandner et al. 2000). These ``debris" disks require a source population of planetesimals to explain their persistence in the face of radiation pressure and Poynting-Robertson drag. Spectral and imaging evidence for inner holes suggests the existence of planetary bodies.

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Despite their initial successes, IRAS and ISO were unable to detect debris disks around solar-mass stars at the distance of the nearest star-forming clouds. However, SIRTF has the requisite sensitivity, as illustrated in the figure at left. A deep survey of the post T Tauri population is needed to uncover the links between the late evolution of disks and planetary systems. The Legacy program c2d, will undertake this survey.