This lecture discusses the martensitic transformation in metals and alloys, focusing on the formation of martensite from austenite, the role of carbon atoms, and the contrast with diffusive transformations. It covers the characteristics, speed, and extent of the transformation, as well as the effects of alloying elements. The process of austenitization, quenching, and the formation of bainite are also explained, along with TTT diagrams and cooling transformation curves.