A shell is a three-dimensional medium that can be represented by the product of a surface and an interval whose dimension is relatively smaller than that of the surface. How to predict the three-dimensional behavior of a shell by the parameters of the surface is the objective of various models found in the literature. This chapter presents in the variational form a new model for thick shells, which includes the variation of the third fundamental form (Gauss deformation) together with those found in the classical theory of Kirchoff-Love, which are widely common in engineering literature. The impact of the contribution of the Gauss deformation in the strain energy is significant when the shell becomes thick. Euler’s equations of this model are established and its best first order approximation contains additional rigidities to the familiar classical ones.