It is well known that the low ductility of nanostructured materials seriously impairs their commercial development. In its turn that mechanical property is associated to the work-hardening behaviour and the vast literature on this relationship is a measure of its importance. This paper presents a short review of the basic models of work-hardening, dealing initially with conventional “coarse” grain metals and alloys, then moving to the behaviour of sub-microcrystalline materials within the bounds of Al alloys and Equal Channel Angular Pressing. Finally, the interrelations of tensile properties, work-hardening behaviour and microstructure are illustrated by data obtained on a precipitation and a non-precipitation hardening Al alloys, namely Al-4%Cu and AA3004. Results show that low temperature aging results in higher strength and high work hardening rate, besides high ductility. The effects of precipitation and of annealing heat treatments are discussed.