In the past decade, there has been an important emphasis in materials science on the production and use of ultrafine-grained materials. These materials offer wide-ranging advantages such as an improvement in strength at low temperatures and enhanced superplastic behavior at high temperatures. New techniques to process these materials have been developed. Good properties have been achieved by powder metallurgy and by techniques of bulk processing. Equal-channel angular (ECA) pressing is a bulkprocessing technique which has led to some remarkable achievements in the production of sub-microcrystalline materials with excellent superplastic properties at low temperatures and high strain rates. When considering the currently available physical and mechanical properties of these materials, it appears that some aspects cannot be explained solely by the very small grain size. In fact, the specific mode of deformation occurring in ECA pressing appears to have an influence on the final properties. This paper reviews the details of this metal working technique and then provides an explanation for the observed microstructures, their thermal stability and their remarkable superplastic properties.