The interaction of NH3 and CH3NH2 with the surfaces of f β-Mo16N7, γ-Mo2N, and δ-MoN films was investigated using thermal desorption spectroscopy. Ammonia temperature programmed desorption (TPD) spectra for the films were similar. Ammonia TPD (adsorption at ∼280 K) produced an NH3 peak at ∼360 K. Some of the NH3 decomposed into H2 and N2. Two H2 desorption peaks were produced: a low temperature peak due to recombination of surface hydrogen and a high temperature peak due to hydrogen that emerged from the nitride subsurface. The N2 desorption spectrum consisted of a peak at ∼340 K and several peaks in the range 500–900 K. The desorption kinetics depended on the structure and composition of the film. 15NH3 TPD experiments indicated that the low temperature N2 desorption peak was due to NH3 decomposition, while the origin of the high temperature peaks was the nitride itself. We believe that nitrogen desorption from the nitride was induced by the presence of hydrogen which altered the Mo-N bonding. Three different CH3NH2 decomposition processes were observed: complete decomposition of CH3NH2 into H2, N2 and C, partial decomposition into HCN, and simple C-N bond hydrogenolysis into CH4 and NH3. The decomposition pathways depended on the structural and compositional properties of the films. All three processes were observed for the β- Mo16N7 (400), β-Mo16N7 (203) and δ-MoN(002) films, while only trace amounts of HCN were detected for the γ-Mo2N(200) film, suggesting that the partial decomposition into HCN was not favored on this surface. The β-Mo16N7 (400) and δ-MoN(002) films had the high selectivities for simple C-N bond cleavage.