Associates of Cu° atoms with anion vacancies v a+ (Cu°v a+centres) are used as luminescent detectors for the study of anion vacancy mobility in KCl crystals. It is found that near 220 K, Cu°v a+ centres may be thermally formed because of the migration of v a+ only to its neighbouring Cu° atom (i.e. the process occurs in {Cu°–v a−} pairs). An analogous process in {Cu+–v a+} pairs results in the creation of Cu+v a+ centres. After Cu+v a+ have trapped electrons released at the thermal destruction of Cu°, Cu°v a+ centres are formed. {Cu+–v a+} and {Cu+–v a+} pairs are produced at low temperatures by the transfer of an F electron onto an impurity ion in irradiation‐generated {Cu+–F} and {Cu2+–F} pairs. If the crystal contains Cu a− centres, Cu°v a+ centres may be formed at T > 370 K by the interaction of mobile VF centres, produced at a thermal dissociation of Cl3 molecular ions, with Cu a− centres. It is proposed that at T < 300 K it is not the isolated but the “associated” anion vacancy that can migrate. This process occurs in the field of some defects and needs a comparatively lower activation energy than the motion of isolated v a+. The isolated or “free” v a+ which are believed to be mobile at higher temperatures, are practically absent in X‐irradiated crystals at T > 250 K due to the interaction of v a+ with mobile cation vacancies or interstitial halide ions as well as due to the thermal association of v a+ with neighbouring lattice defects.