Due to its affordability, excellent stiffness-to-density ratio, and predictable forming characteristics, steel has historically dominated the material selection for vehicle body structures. As light-weighting has gained momentum due to more stringent vehicle emissions standards, the usage of Advanced High Strength Steels (AHSS) has proliferated during the past two decades. In the last decade, significant efforts have been made in developing the “third generation” of AHSS with strength-ductility combinations significantly better than in the first generation AHSS. A paradigm changing nanostructured 3rd Generation AHSS has been developed by NanoSteel that will be described with a focus on the new mechanisms, enabling structures, and resulting mechanical properties. New mechanisms include nanoscale structure formation through a Static Nanophase Refinement mechanism at high temperatures and the ability to strain harden during cold deformation with formation of nanoscale precipitates through a Dynamic Nanophase Strengthening mechanism. The enabling structural pathway is much different than that found in conventional steels and the steps in creating the targeted characteristic nanoscale structures will be detailed including the specific microstructural pathway for a Class 2 non-stainless NanoSteel 3rd Generation AHSS. Due to the new enabling mechanisms and formation of novel structure types, a wide range of tensile properties can be provided within and beyond the targeted 3rd Generation AHSS range. The new NanoSteel Class of AHSS is expected to extend the existing technological window for cold formable steels in advanced automobile design and manufacturing in body-in-white and other structural applications.