Poisson's ratio for anisotropic elastic materials can have no bounds

Poisson's ratio for isotropic elastic materials is bounded between -1 and 1 / 2 . It is shown that Poisson's ratio for anisotropic elastic materials can have an arbitrarily large positive or negative value under the prerequisite of positive definiteness of strain energy density. The large Poisson's ratio for cubic materials is physically realistic because the strains are bounded.