When polarized light passes through a material in the presence of a strong magnetic field, birefringence is observed. This is known as the Cotton-Mouton effect. Owing to the increasing sophistication of both experimental and computational techniques, this particular aspect of magneto-optics has been investigated increasingly in the last few years. In this review the basic facts concerning both experiment and theory are discussed and tables summarizing all currently known gas-phase data are presented.

Multiconfigurational self‐consistent field (MCSCF) response is used to study the electric field dependence of magnetizabilities and nuclear shielding constants for N₂, C₂H₂, HCN, and H₂O. London perturbation‐dependent atomic orbitals are used to ensure gauge origin independence. The computed magnetizabilities and shielding derivatives show a strong electron correlation dependence. The N₂ results confirm the conclusions of previous ab initio studies. For the other molecules, this is the first study of the above magnetic properties beyond the SCF approximation.