This Article reports the result of a computational study on the reaction of hydrazoic acid and trimethylindium (TMIn), coadsorbed on TiO2 rutile (110) surface. The adsorption geometries and energies of possible adsorbates including HN3-In(CH3)(3)(a) and its derivatives, HN3-In(CH3)(2)(a), N-3-In(CH3)(2)(a), N-3-In(CH3)(a), and N-In(a), have been predicted by first-principles calculations based on the density functional theory (DFT) and the pseudopotential method. The mechanisms of these surface reactions have also been explicitly elucidated with the computed potential energy surfaces. Starting from the interaction of three stable HN3 adsorbates, HN3-O-b(a), H(N-2)N-O-b(a), and Ti-NN(H)N-O-b(a), where O-b is the bridged O site on the surface, with two stable intermediates from the adsorption and dissociative adsorption of TMIn, (H3C)(3)In-O-b(a) and (H3C)(2)In-O-b(a) + H3C-O-b(a), InN products can be formed exothermically via four reaction paths following the initial barrierless In-atom association with the N atom directly bonded to H, by CH4 elimination (with similar to 40 kcal/mol barriers), the InN-N bond breaking and the final CH3 elimination or migration (with < 20 kcal/mol barriers). These Langmuir-Hinshelwood processes producing the two most stable InN(a) side-on adsorptions confirm that HN3 and TMIn are indeed very efficient precursors for the deposition of InN films on TiO2 nanoparticles. The result of similar calculations for the reactions occurring by the Rideal-Eley mechanism involving HN3(a) + TMIn(g) and HN3(g) + TMIn(a) indicates that they are energetically less favored and produce the less stable InN(a) with end-on configurations.