The growth in the use of ultraviolet and soft x‐ray synchrotron radiation has been remarkable in the past decade. The 1970s saw the number of worldwide scientific and technological users of ultraviolet and x‐ray synchrotron radiation increase from fewer than perhaps twenty to well over a thousand. In a single decade, an unwanted byproduct of high‐energy electron storage machines has turned into the driving force for building a new generation of electron storage rings designed specifically as radiationsources. (See the article by Ednor Rowe, on page 28.) Several new machines with electron energies of 700–1000 MeV are being constructed specifically as sources of ultraviolet and soft x‐ray radiation in the regions below about 1000 eV (above about 12 Å in wavelength).
Photon‐stimulated excitations of electrons, photons and ions provide a basis for innumerable spectroscopy techniques as well as for important technological tools.