Fundamental mechanisms of grain refinement during equal-channel angular pressing (ECAP) and multiple isothermal forging (MIF) are analyzed and compared. Based on this analysis, deformation methods of nanostructuring are classified into severe plastic deformation and mild plastic deformation methods. It is demonstrated that MIF is a versatile method allowing for a production of bulk and sheet nanostructured semi-products with grain size down to 50 nm and applicable to various metals and alloys. Novel mechanical properties of bulk nanostructured materials produced by this method are presented. The ways of their structural and functional applications are discussed.