Current works on the defect formation by ionizing radiation in alkali halides are reviewed. In the first place discussion is made on the self-trapped exciton (Vk e) which leads to the formation of the Frenkel defects. Several experimental observations are presented which indicate that (Vk e) producing σ and π-emissions are not the precursors of the Frenkel pairs. The second problem is on the dynamic motion of the interstitial halogen atom possessing the kinetic energy imparted through the non-radiative recombination of (Vk e). Experimental results of the temperature dependence of the range of the dynamic motion in various alkali halides are surveyed and its correlation with the temperature dependence of the production yields of defects is discussed. Finally the mechanism of the interstitial stabilization and its effects on the kinetics of defect production is discussed