The application of severe plastic deformation to polycrystalline metals provides an opportunity to achieve substantial grain refinement, often to within the submicrometer or nanometer level. Several methods are available for imposing this deformation including Equal-Channel Angular Pressing (ECAP) in which a sample is pressed repetitively through a die in order to impose a large strain by shear and High-Pressure Torsion (HPT) where a disk-like sample is subjected to torsional straining under a high pressure. This paper reviews these two techniques and then presents a detailed appraisal of the application of ECAP to aluminum-based alloys. Special attention is given to the experimental parameters associated with achieving a uniform and ultrafine-grained structure. It is shown that processing by ECAP provides an opportunity for increasing the strength and toughness of aluminum alloys at ambient temperature and also it may provide an opportunity for achieving good formability at relatively rapid strain rates at elevated temperatures. This latter result has important implications for the superplastic forming industry.