The development of modern, sustainable materials is based on the tailoring of the microstructure to achieve the required properties by producing the ultrafine materials using phase transformation or advanced processing such as severe plastic/shear deformation, utilizing cluster/nano-twinning/solutes/dislocations strengthening mechanisms, formation of non-stochastic phases and modelling. While historically this was performed at the micrometre scale length there is now the scope to undertake characterization at the nanoscale or atom scale. The presentation reviews recent work related to the development of ultrafine and nanoscale microstructures in steel as well as changes at shorter scale lengths. It includes formation of clusters in specifically designed dual-phase steel, solute segregation at the interface during austenite to ferrite transformation in nano ferritic steel (Fig. 1), segregation at grain boundary and dislocations in bake hardened steel, formation of nano-layers of bainitic ferrite and retained austenite in nano-bainitic steel (Fig. 1), formation of stacking faults and nano-twins during deformation in twining induced plasticity steels etc. The correlative microscopy approach using EBSD scanning, transmission electron (TEM), and atom probe microscopy (APT) on the samples prepared by site-specific method. This enables to design novel alloys and processing schedule to manipulate the properties.