Metallic plate dampers, when incorporated into a structure, provide one of the most effective energy dissipation mechanisms available during an earthquake. Increasingly, they are applied in the seismic retrofit of structures which are found to be deficient. The design of these devices, however, has been largely based upon experiments and macroscopic modeling. In order to gain more insight into the response behavior of metallic plate dampers, a microscopic mechanistic approach is followed in this paper. Included is the development of an inelastic constitutive model for the damper material. Numerical results obtained for a class of metallic plate dampers are presented and comparisons are made with experimental data for validation of the mathematical model. It is also shown that this approach sheds light on several aspects of the damper response which heretofore have not been addressed adequately.