The existence of a theoretical continuum multiphysics infrastructure for modeling the behavior of electroactive polymers and ionic polymer metal composites is essential for the design, material qualification and material certification for sensing, actuation and energy harvesting applications. The present chapter summarizes a continuum multiphysics methodology for modeling the behavior of arbitrarily shaped ionic continua under multi-field influence at the macro-length scale. The analytical implementation of this methodology addresses the generation of both the constitutive and the field evolution equations by appropriate use of continuum mechanics, irreversible thermodynamics and electrodynamics. We apply this methodology for the case of electric multicomponent anisotropic hygrothermoelasticity that generates a constitutive model and the associated field equations for a large class of materials capable of electromechanical actuation and sensing. A specialization of this theory for isotropic and bi-component electrohygrothermoelastic materials is provided in terms of the relevant field equations.