This article summarizes a Splinter Session at the Cool Stars XV conference in St. Andrews with 3 review and 4 contributed talks. The speakers have discussed various approaches to understand the structure and evolution of the gas component in protoplanetary disks. These ranged from observational spectroscopy in the UV, infrared and millimeter,through to chemical and hydro-dynamical models. The focus was on disks around low-mass stars, ranging from classical T Tauri stars to transitional disks and debris disks. Emphasis was put on water andorganic molecules, the relation to planet formation, and the formation of holes and gaps in the inner regions.