First, a three-dimensional anisotropic free body is considered which will provides six stresses and six strains, which constitute a 6x6 matrix of stress/strain relations. Next, we apply each component of the matrix in equilibrium and stress displacement relation after non-dimensionalizing all the variables to allow asymptotic expansion and integration. Then we can derive the first approximate shell theory of anisotropic materials. The integration procedure over thickness will allow laminated anisotropic wall materials. The derived governing equation of the bending theory is unique; it is useful for identifying stress and displacement variation as well as the location of stiffeners for external pressure loading.