When Ag{111} is exposed to NO at 40 K, monolayer adsorption is followed by multilayer (NO)(2) formation. Heating to 60 K results in the desorption of the dimer multilayer, leaving a monolayer on the surface. Using isotopes, the monolayer has also been characterized as dimers, which have the N-N axis coplanar with the surface. At 70 to 90 K, N2O is formed from (NO)(2) on the Ag{111} surface. Further heating to 120 K results in the desorption of the N2O. The reactive species is thus shown to be the adsorbed dimer, which cannot be formed at higher temperatures on exposure to NO because the surface coverage is too low. The monomer, adsorbed NO, is thus weakly adsorbed, in agreement with expectation.