X-ray Absorption Fine-Structure (XAFS) is an element-specific spectroscopy in which measurements are made by tuning the X-ray energy at and above a selected core-level binding energy of a specified element. Although XAFS is a well established technique providing reliable and useful information about the chemical and physical environment of the probe atom, its requirement for an energy-tunable X-ray source means it is primarily done with synchrotron radiation sources and so is somewhat less common than other spectroscopic analytical methods. XAFS spectra are sensitive to the oxidation state and coordination chemistry of the selected element, and the extended oscillations in the spectra are sensitive to the distances, coordination number, and species of the atoms immediately surrounding the selected element. Because it is element-specific, XAFS places few restrictions on the form of the sample, and can be used in a variety of systems and bulk physical environments, including crystals, glasses, liquids, and heterogeneous mixtures. Additionally, XAFS can often be done on low-concentration elements (typically down to a few ppm), and so has applications in a wide range of scientific fields, including chemistry, biology, catalysis research, material science, environmental science, and geology.