Observations of circumstellar disks with infrared interferometry

The structure and composition of circumstellar disks around young stars is one of the areas in which infrared interferometry has had a major impact. I will review the observational progress in this field starting from the earliest observations of T Tauri, Herbig Ae/Be and FU Ori objects with smaller interferometers. Highlights of recent work include measurements of the inner disk size across 5 orders of magnitude in stellar luminosity, characterization of the dust composition as a function of radius in Herbig disks, high spectral resolution observations of gas emission and closure phase measurements of structure in disks. These observations have challenged models of disk structure and as the only direct probe on AU scales will continue to provide essential input in our understanding of the formation of stars and planets