Particle Induced X-Ray Emission (PIXE) is an analytical method which relies on the spectrometry of characteristic x-rays emitted by the target elements due to the irradiation of a high energy ion beam (typically 1-2 MeV of H or He). PIXE can identify various constituents in a compound target. Since there is little overlapping of the characteristic x-rays for different elements, simultaneous detection of complicated multi-elements sample is possible. Quantitative analysis is also possible with the appropriate corrections to absorption and x-ray yields. Trace element analysis using PIXE has a detection limit orders of magnitude lower than can be attainable by x-ray spectrometry techniques using electron excitation. Under favorable conditions, a detection limit ~1 ppm for thin foils and ~10 ppm for thick samples can be achieved. PIXE has been successfully applied to solving problems in many different fields, including corrosion and oxidation, semiconductors, metallurgy, thin films, geoscience, air pollution and atmospheric science, biology, medicine, art, archaeology, water analysis, and forensic science.