The electric field induced alignment of substitutional OH − ions in a variety of alkali halide crystals was studied, using electro-optical and electro-caloric techniques. As basis for the electro-optical studies, the u.v. absorption of OH − in various crystals was thoroughly investigated at different temperatures, and in several cases oscillator strength values were determined. The energy position of the u.v. absorption of OH − in 13 alkali halides follows closely an Ivery-relation, which is discussed in terms of a charge-transfer model. The observed electric field induced zero-moment changes of the u.v. absorption, which depend strongly on light polarization, field direction and temperature, can be quantitatively accounted for by a paraelectric alignment model of permanent dipoles with moment p. The anisotropy of the OH − electro-dichroism reveals <100> dipole orientation in NaCl, KCl, KBr, RBCl, RbBr and RbI, <110> orientation in KI, and <111> orientation in CsBr. The determined dipole moment values p show little variation with the host material, which excludes sizeable contributions to p from off-center shifts of the OH − ion. The observed saturation of the electro-dichroism indicates a peculiar ‘mixed’ polarization behavior of the optical transition, which will be discussed. Reversible electro-caloric measurements, performed on several OH − systems, reveal a field dependence and anisotropy in the high field range, which yield dipole orientation and dipole moment values in agreement with the electrooptical results.