A theoretical model has been developed to study the optical properties of metallic multishell structures on the nanometer scale. The Mie theory was generalized for multiconcentric spherical shell nanostructures and employed to determine the effects and importance of the different parameters of the system such as thickness, size, and other material properties, for instance, the medium index of refraction. A unique hollow gold-silver double-shell structure is used as an example to test the model developed with recent experiments. The surface plasmon resonance (SPR) absorption spectrum of this structure has been calculated as a function of various parameters, including shell thickness and diameter. Using parameters similar to those previously reported experimentally, very good agreement has been found between calculated and experimentally measured SPR spectra, which validates the model. The results provide new insights into the fundamental properties of complex metal nanostructures that give us the ability to control the optical response, which has important implications in the synthesis of new metal nanostructures as well as their application in emerging technologies.