Nanotechnology has become an overused adjective, but there has been justified excitement in the context of structural materials. A class of iron alloys has been discovered in which a high density of strong interfaces can be created by heat-treatment alone. The packing of interfaces is so large, and the fact that there is an intrinsic work hardening mechanism in the structure, leads to remarkable properties. The genesis of this structure, its commercialization, the new science associated with the discovery, and its limitations are all explored in this short review.