Analytical investigations carried out on Austrian medieval window glass by means of various instrumental analytical techniques yielded results similar to those obtained for stained window glass from Great Britain, France and other European countries. Depending on the chemical composition and particularly on the silica content of the glass three types of deterioration were observed for Austrian medieval stained glass: crusted, pitted, and apparently unweathered glass. In addition to those glasses with a high silica content, the dark green window glasses containing lead and phosphorus oxides also show a smooth and scarcely weathered exterior surface. Nevertheless, a weathering mechanism governed by an ion exchange process can be determined by surface analytical investigations. The alkali ions such as potassium and sodium as well as the alkaline earth ions (calcium, magnesium, barium) and lead are exchanged by hydrogen bearing species, leading to a leached layer on the glass surface. The analytical techniques used are briefly described and their potentials for the material characterization of archaeological and art glasses are discussed.