Adsorption and reactions of NO on clean and CO-precovered Ir(1 11) were investigated by means of X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HR-EELS), infrared reflection absorption spectroscopy (IRAS), and temperature-programmed desorption (TPD). Two NO adsorption states, indicative of fcc-hollow sites and atop sites, were present on the Ir(1 11) surface at saturation coverage. NO adsorbed on hollow sites dissociated to N-a and O-a at temperatures above 283 K. The dissociated Na desorbed to form N-2 by recombination of N-a at 574 K and by a disproportionation reaction between atop-NO and N-a at 471 K. Preadsorbed CO inhibited the adsorption of NO on atop sites, whereas adsorption on hollow sites was not affected by the coexistence of CO. The adsorbed CO reacted with dissociated O-a and desorbed as CO2 at 574 K.