The work is devoted to the development of the bimoment theory and the method for calculating thick plates in the framework of the three-dimensional theory of elasticity. The basic relations and equations of motion of the plate are given, constructed with respect to forces, moments and bimoments, arising from the nonlinearity of the law of distribution of displacements and stresses over its thickness. Bending and vibrations of isotropic and orthotropic plates are considered as an example of calculation. The resulting solution showed the efficiency and accuracy of the proposed bimoment theory in assessing the stress-strain state of thick plates. Figs.: Refs.: 11 titles.
 Keywords: thick orthotropic plate, three-dimensional theory of elasticity, bi-moment theory, bending and vibrations, stress-strain state.