The main objective of this thesis is to provide an irreversible thermodynamics framework to describe and predict the work hardening and stress-strain phenomena occurring in single grained and polycrystalline metals. Models to quantitatively describe these are presented. Especial emphasis is placed on the understanding of the evolution of dislocations. The models are applied to pure metals and single phase alloys with FCC or BCC structures over a wide range of temperatures, strain rates and grain sizes.