The interaction of NO with a Ni (111) surface was studied by means of LEED, AES, UPS and flash desorption spectroscopy. NO adsorbs with a high sticking probability and may form two ordered structures (c4 × 2 and hexagonal) from (undissociated) NO ad. The mean adsorption energy is about 25 kcal mole . Dissociation of adsorbed NO starts already at −120°C, but the activation energy for this process increases with increasing coverage (and even by the presence of preadsorbed oxygen) up to the value for the activation energy of NO desorption. The recombination of adsorbed nitrogen atoms and desorption of N 2 occurs around 600 °C with an activation energy of about 52 kcal mole . A chemisorbed oxygen layer converts upon further increase of the oxygen concentration into epitaxial NiO. A mixed layer consisting of N ad + O ad (after thermal decomposition of NO) exhibits a complex LEED pattern and can be stripped of adsorbed oxygen by reduction with H 2. This yields an N ad overlayer exhibiting a 6 × 2 LEED pattern. A series of new maxima at ≈ −2, −8.8 and −14.6 eV is observed in the UV photoelectron spectra from adsorbed NO which are identified with surface states derived from molecular orbitals of free NO. N ad as well as O ad causes a peak at −5.6 eV which is derived from the 2p electrons of the adsorbate. The photoelectron spectrum from NiO agrees closely with a recent theoretical evaluation.