The crystal distortion which arises from the Jahn-Teller effect is discussed in several examples. In thecase of compounds containingCu2+orMn3+at octahedral sites, the lowest orbital level of these ions isdoubly degenerate in the undistorted structure, and there is no spin-orbit coupling in this level. It is shownthat, introducing a fictitious spin to specify the degenerate orbital states, we can discuss the problem byanalogy with the magnetic problems. The “ferromagnetic” and “antiferromagnetic” distortions are discussedin detail. The transition from the distorted to the undistorted structure is of the first kind for theformer and of the second kind for the latter. Higher approximations are discussed briefly. In compounds likeFeO, CoO, andCuCr2O4, the lowest orbital level is triply degenerate, and the spin-orbit coupling is presentin this level. In this case the distortion is dependent on the magnitude of the spin-orbit coupling relativeto the strength of the Jahn-Teller effect term. The distortion at absolute zero temperature and its temperaturedependence are discussed.