The different important stages of the development of proton induced X-ray emission (PIXE) spectrometry utilised with success
since 1976 at Liège University are outlined. The methodological efforts (irradiation, target preparation, calibration, matrix
effect corrections) to improve quantitative trace element analysis are emphasized. Examples of applications in geological,
biomedical and environmental sciences are selected in order to illustrate the potential of the technique in these fields.