The adsorption of phthalic anhydride on clean and oxygen predosed Cu{110} surfaces has been studied by Fourier transform infrared spectroscopy in the temperature range 95−300 K. Further characterization of the adsorbed species and its thermal stability on these surfaces has been obtained from thermal desorption measurements. A variety of species are produced on the clean surface including the parent molecule, one in which the anhydride ring has been cleaved and one following the loss of a CO unit which is the stable form at room temperature. In the presence of oxygen, CO loss is prevented and, instead, a phthalate species is formed. Infrared spectroscopy is ideally suited to identify these species and their orientation, which varies both with coverage and temperature in a complex manner. Thermal breakdown of the molecule occurs above 530 K on the clean surface to produce a variety of gas-phase products including benzene. The breakdown occurs at a somewhat higher temperature (585 K) in the case of the oxygen-predosed surface and leads to an explosive release of the products into the gas phase.