Abstract
Fundamental behavior of auxetic solids is laid down in terms of linear anisotropic constitutive relationship, followed by the derivation of Poisson’s ratio bounds for isotopic solids in 3D and 2D cases. Increasing simplifications are then imposed on the compliance matrices of the complete anisotropic solid until linear isotropic case is obtained, whereby special trends are observed for Poisson’s ratio of −1, −2/3, −1/2 and 0, followed by distinct moduli ratio that separates auxetic solids from conventional ones. Thereafter the chapter explores large elastic deformation, anisotropic crystals, elastoplasticity and viscoelasticity of auxetic media.