The surface chemistry of hydrazoic acid (HN3) on Al(111) was investigated from 100 to 800 K with temperature-programmed desorption, infrared reflection-absorption spectroscopy (IRRAS), Auger electron spectroscopy, and low-energy electron diffraction (LEED). IRRAS suggests that the first monolayer dissociatively chemisorbs as N-2(ads) and NH(ads) at 120 K. Subsequently, HN3 adsorbs molecularly in two phases, a physisorbed second layer and a condensed multilayer. In the former, the N-3 chain of the HN3 is aligned normal to the substrate surface, while in the latter HN3 exhibits a random orientation. Molecular HN3 desorbs at 125 K, and two decomposition products, N-2 and H-2, desorb at 295 and 615 K, respectively. Mixed-isotope desorption experiments show that N-2 is derived from an intact NN species, rather than from recombinative desorption of N(ads), and is consistent with the IRRAS observation of chemisorbed N-2. IRRAS indicates that the NH species dissociates into N(ads) and H(ads) above 320 K, with H-2 thermal desorption resulting from dissociation of the AlHx (1 less than or equal to x less than or equal to 3) moiety. After the sample was annealed at 800 K, N was observed with Auger spectroscopy. The partially nitrided Al(111) surface exhibits a concentric, double hexagonal LEED pattern indicating AlN(0001) islands. IRRAS indicates that the islands are Al-terminated and capped with H at temperatures as high as 700 K.