Design of metastable retained austenite (RA) has been one of the most key issues in the development of advanced high strength steels (AHSS) as mechanical properties of AHSS are linked to the amount of RA and its stability. In the past decades, several novel concepts, e.g. Quenching & Partitioning(Q&P), Reverted austenite transformation (RAT), isothermal bainitic transformation (IBT), have been successfully proposed to obtain RA in AHSS. However, up to now, optimization of processing parameters and alloy composition in the above concepts is primarily by “trial and error” experiments or thermodynamic calculations. In this talk, we will present a physical model, in which thermodynamics and transformation kinetics are carefully considered, to design RA in AHSS. The effect of processing parameters and alloy composition in the Q&P, RAT and IBT concepts on the amount of RA and its stability will be analyzed, and a comparison among these three concepts is made.