The joint application of experimental techniques, such as MIKE, CAD, and FT-ICR spectrometry, and computational methods (DFT and QCISD(T)) has allowed preparation and characterization of gaseous XeNO3+ and XeNO2+ ions. The most stable structure of XeNO3+ has the XeONO2 connectivity, with a relatively short (2.088 Angstrom) Xe-O bond, and represents the gas-phase counterpart of Xe(II) nitrate, previously observed in solution. The XeNO2+ cation is best characterized as a [Xe-NO2](+) complex, with a:large (3.018 Angstrom) Xe-NO2 separation and a relatively low dissociation energy, 10.8 kcal mol(-1). The reaction of XeNO3+ with selected nucleophiles, including CH3OH, C2H5NO2, CH3COCH3, CH3CN, and C2H5CN, investigated by FT-ICR mass spectrometry, characterizes the ion as a nitrating agent. The unimolecular and collision-induced fragmentation of XeNO3+ and XeNO2+ is discussed.