An excess of half-jogs or of isolated vacancies of one sign on the core of an edge dislocation in an alkali halide will result in the dislocation being charged. This charge is calculated for a dislocation in equilibrium with both anion and cation vacancies, using a model which includes the free energy of the defects on the dislocation core as well as the electrostatic energy of the dislocation surrounded by its compensating charge cloud. The theory is illustrated for NaCl at around 700°K. In most cases it is likely that the charge is limited not so much by the electrostatic energy as by the way in which the charge can be accommodated on the dislocation.