This thesis presents a new methodology to quantify mechanical elastic constants of polycrystalline thin films using X-ray diffraction under static conditions. The approach is based on the combination of X-ray diffraction substrate curvature and sin square psi methods. It is shown how to extrapolate the mechanical elastic constants from X-ray elastic constants considering crystal and macroscopic elastic anisotropy. A general formula is presented which can be used to determine a reflection hkl and its corresponding value of the X-ray anisotropic factor 3 Gamma hkl for which the X-ray elastic strain is equal to the mechanical strain. The method is applied to Cu/Si(100), CrN/Si(100) and TiN/Si(100) thin films deposited onto monocrystalline Si(400) substrates at room temperature. It is demonstrated that, for ber textured thin films, the 3 Gamma hkl value depends strongly on the fiber texture sharpness and the amount of randomly oriented crystallites. The advantage of the new technique remains in the fact that mechanical moduli are determined non-destructively and represent volume-averaged quantities.