[en] In the 21st century, the X-ray fluorescence (XRF) technique is widely used in process control, industrial applications and for routine elemental analysis. The technique has a multielement capability capable of detecting elements with Z ≥ 10, with a few instruments capable of detecting also elements with Z ≥ 5. It is characterized by a non-destructive analysis process and relatively good detection limits, typically one part per million, for a wide range of elements. The first commercial XRF instruments were introduced to the market about 50 years ago. They were the wavelength dispersive X ray fluorescence (WDXRF) spectrometers utilizing Bragg’s law and reflection on crystal lattices for sequential elemental analysis of sample composition. The advances made in radiation detector technology, especially the introduction of semiconductor detectors, improvements in signal processing electronics, availability and exponential growth of personal computer market led to invention of energy dispersive X ray fluorescence (EDXRF) technique. The EDXRF is more cost effective as compared to WDXRF. It also allows for designing compact instruments. Such instruments can be easily tailored to the needs of different customers, integrated with industrial installations, and also miniaturized for the purpose of in-situ applications. The versatility of the technique has been confirmed in a spectacular way by using the XRF and X-ray spectrometric techniques, among few others, during the NASA and ESA missions in search for the evidence of life and presence of water on the surface of Mars. The XRF technique has achieved its strong position within the atomic spectroscopy group of analytical techniques not only due to its versatility but also due to relatively low running costs, as compared to the commonly used methods, e.g., atomic absorption spectrometry (AAS) or inductively coupled plasma atomic emission/mass spectrometry (ICP-AES/MS). Presently, the XRF technique together with X ray diffraction (XRD) constitute about one third of the worldwide market for atomic spectroscopy or about $630 million. In the next few years this market is expected to expand at a rate from 4.7% to 5.5% per year. This growth is generated by improving economic conditions, especially in Asia and also due to increased investments for instrumentation for environmental monitoring and testing worldwide, in industrialized nations as well as in developing countries. Also other X-ray related techniques, requiring more sophisticated instrumentation, are finding routine applications. In particular the ion beam analysis (IBA) methods such as proton induced X-ray emission (PIXE) are of importance in air pollution studies. The increasing number of synchrotron facilities enables for a routine use of X ray microbeam techniques in environmental studies, material research, structural research, and many other fields. (author)