Resonant ionization mass spectrometry (RIMS) is an emerging analytical technique that can accomplish very sensitive and unambiguous identification of elemental impurities in bulk materials, on surfaces, and in particulates. Because the technique combines high sensitivity and selectivity, the concentration of various contaminants may be determined at and below the part-per-billion (ppb) level. Moreover, such determinations can be quantitative even in complex matrices, and concentration maps at high lateral resolution have been obtained.