Multifield potentials and extremum theorems are investigated with reference to evolutive processes in rate-dependent plasticity. A general strategy is followed by casting the non-linear field equations and the constitutive multivalued equations into a rate-dependent plastic structural operator governing the model problem. By following a consistent procedure multifield potentials are derived which govern the evolutive problem in rate plasticity. A multifield variational principle is presented which is able to provide the support for a variationally consistent development of computational algorithms in finite element applications.