Among advanced high strength steels, there has been a particular interest in TRIP steels because of their unique combination of strength and ductility. These steels are characterized by complex microstructures containing various amounts of ferrite, bainite, retained austenite and perhaps martensite. Undoubtedly, therefore, understanding the transformation behavior of these steels is necessary in developing these products. Recently, the focus has been on aluminum based TRIP steels because of their relative ease of coatability. However, the search continues to obtain higher and higher strength in these steels without further additions of silicon. The addition of niobium to aluminum based steel compositions has been the object of recent studies at Ispat Inland Research Laboratories. The effect of niobium on the phase transformation behavior in these steels is reported in this paper. In particular, the kinetics of austenite formation as well as the CCT and TTT behaviors of these steels have been studied in detail. The results of these studies should form an important basis for the development of these transformation-based steels.