Alkali halides containing substitutional OH- ions have become prominent and well investigated examples and model systems for paraelectric and paraelastic crystal substances. Controlled doping between 10-6 and 10-2 allows the study of both interaction-free and interacting dipole systems with various experimental techniques. Here the optical and caloric techniques are reviewed. The basis for electro-optical and elasto-optical work is a detailed knowledge of the optical absorption itself. This is reviewed first, covering the electronic (~ 6 eV), vibrational (~ 0.45 eV) and the recently discovered direct librational absorption (~ 0.04 eV) of the OH- center. The electro- and elasto-optical effect (change of optical absorption under applied electric and elastic fields) reveals for most investigated cases that the dipoles are confined to the < 100 > directions by the octahedral crystalline potential. Values for the effective electric and elastic dipole moment and the optical anisotropy of the center are obtained from these experiments. Using the electro-caloric effect and varying the rise- and decaytime of the applied electric field, the dipole-lattice relaxation time can be directly measured. Recent experiments on six different alkali halides show a considerable dependence of this relaxation time on the host lattice, varying between 2 × 10-5 and 2 × 10-9 sec at 2 °K. From the field- and temperature-dependence of the dipole-lattice relaxation time, conclusion can be drawn about the coupling mechanism between dipole and phonons. Interaction effects among concentrated OH- dipole systems and among systems of diluted OH- dipoles and charged point defects (Frenkel pairs) were quantitatively studied, using the electro- and elasto-optical as well as the electro-caloric technique