The overarching objective of this project is three-fold: 1) derive and numerically implement the homogenized equations describing the macroscopic electro- and magneto-mechanical response of elastomers filled with compressible and incompressible fluid inclusions directly accounting for the mechanical, electric, and magnetic interfacial forces at the elastomer/fluid-inclusion interfaces; 2) deploy the derived homogenized equations to guide the design of fluid inclusions that lead to porous electrets and elastomers filled with liquid-metal and ferrofluid inclusions with exceptional macroscopic electro- and magneto-mechanical properties; and 3) fabricate and characterize the microscopic and macroscopic properties of representative classes of electrets with electrically charged gas-filled pores, elastomers filled with liquid-metal inclusions, and elastomers filled with ferrofluid inclusions. The theoretical component involves new mathematical results and their associated numerical implementation that directly account for the rapid spatial variation (at the microscopic scale of the fluid inclusions) of space electrical charges and interfacial forces in the homogenization of the governing equations, namely, balance of momenta and Maxwell's equations. The experimental component, on the other hand, entails the synthesis of these new classes of multifunctional material systems and the development of new experiments that leverage in-situ X-ray tomography and thermally stimulated depolarization current measurements to extract the interfacial forces and space charge content and behavior at the elastomer/fluid-inclusion interfaces.