Understanding the main relationships between the microstructure parameters controlling the strength and ductility of low temperature bainitic microstructures is of considerable importance for further development of these grades. Although the microstructure essentially consists of solely two phases, bainitic ferrite and retained austenite, the complexity of the different microstructural characteristics, the natural consequence of its unique transformation mechanisms, might not provide with one unique answer, but a set of several parameters interdependent among them. This paper will deal with some of these relationships' microstructure properties, strength, and ductility, with special emphasis in the mechanical stability (TRIP effect) of retained austenite.