2-Azidoacetic acid (N3CH2CO2H) has been synthesized and characterized by a variety of spectroscopic techniques, and the thermal decomposition of this molecule studied by matrix isolation infrared spectroscopy and real- time ultraviolet photoelectron spectroscopy. The results are consistent with the vapor phase thermal decomposition following a pathway involving concerted ejection of molecular N2 and the simultaneous formation of CO2 and methanimine (CH2NH). No evidence was found for the presence of intermediates such as the nitrene NCH2CO2H or the imine HNCHCO2H. At higher temperatures. CH2NH further decomposes to give HCN and H2.