An overview of different methods for the derivation of extended continuum models is given. A
gradient plasticity theory is established in the context of small deformations and single slip
by considering the invariance of an extended energy balance with respect to Euclidean
transformations where the plastic slip is considered as an additional degree of freedom.
Thermodynamically consistent flow rules at the grain boundary are derived. The theory is
applied to a two- and a three-phase laminate.
