The site of Hasanlu is located southwest of Lake Urmia (Lake Rezaiyeh) in the province of Western Azerbaijan, northwest Iran. Excavations carried out by Dr. R. H. Dyson, Jr. of the University of Pennsylvania from 1957 to 1977 of the Iron Age levels at Hasanlu yielded a larges number of glass beads, as well as glass vessels, and glass furniture inlays or wall fittings. Sampling of many of these pieces was limited to weathered areas, requiring the use of a microanalytical technique to characterize the glass. Electron microprobe and wavelength dispersive analysis were used th characterize the chemical compositions of the glasses of Hasanlu. The glasses are soda-lime-silica in composition, containing about 17-21 wt% soda and 2-8 wt% lime. Of 51 glasses analyzed to date, 47 contain about 1-6 wt% of magnesia and 1-4 wt% potash, indicative of a plant ash source of alkali. Four glasses contain less than 1 wt% each of magnesia and potash, suggesting that these may have been made with a mineral alkali source like natron. At least 35 glasses contain inclusions of partly reacted batch materials. In blue transparent to translucent, black translucent, and yellow opaque glasses, large, 0.2 mm diameter, droplets of alkali sulfates exhibit features that indicate they were an immiscible liquid coexisting with a surrounding silicate liquid. These sulfate droplets, which appear to be relatively common in the glasses found at Hasanlu, are probably the scum or gall that can form during melting of poorly prepared plant ash. Remnants of original raw colorants occur in a few glasses. Many of the black glasses contain polymetallic sulfides of different combinations of lead, copper, antimony, and iron. These inclusions and the glass chemistry are used to interpret the origin and processing of the batch materials, and the conditions under which the materials were melted.