The self‐diffusion of alkali ions in alkali silicate glasses is discussed in terms of the formation, migration, and ultimate annihilation of defects. These defects exhibit a combination of the properties exhibited by Frenkel defects in alkali halides and Bjerrum defects in ice, and are treatable by many of the analytical techniques which are applicable to defects in crystalline solids. By utilizing the defect concept, relationships between self‐diffusion, ac and dc conductivity, and orientational polarization are obtained.