The book describes the methods of calculation of three-layer structures. The shell theory assumes a general theory of straight three-layer rods. Here are the main tasks that are currently developed for the case of homogeneous rods. The author describes the theory of the gentle shells of the final deflection, which is a generalization of the classical theory of the gentle shells. The equations of this theory are used to determine the critical loads and frequencies of the eigen oscillations of cylindrical, spherical, conical and toriform shells under various external influences. The theory of the so-called half-momentless cylindrical three-layer shells develops. The theory of three-layer non-hollow shells of general appearance at finite deflections. is given.