Research on the physical metallurgy of steels, whose top is dated more than a century, has not allowed a thorough understanding of the physics that controls the processes and the properties of conventional materials. Different allotropic forms of iron and in many ways and mechanisms of phase transformations, give the steel a huge versatility from a variety of microconstituents and properties that may be exploited industrially. However, the various requests and requirements identified by the industry, which at first arise as contradictory, such as the need for resistance and formability, has fueled the development of microstructural effects in complex materials that have come to provide a reconciliation of these required properties. The design of new materials is always associated with the new demands and challenges of the market for steel. From the correct formulation of alloying elements and defining an appropriate thermomechanical processing, it becomes possible to combine many possibilities of properties from the coexistence of different structural components. In this work, we will describe briefly three types of steels of this kind of versatility, among the several options that have emerged in the recent history of Steel: TRIP steels, Biphasic steels and TWIP steels.