Martensite is the hardest form of steel, stabilized when the rapid quenching of Fe-C steel traps interstitial carbon atoms in the high-temperature face-centered cubic (FCC) phase of iron. This trapping of carbon causes the FCC phase to distort into a tetragonal structure through a “diffusionless” shearing mechanism, known as the martensitic transformation. During this process, the material undergoes multiple twinning to minimize stresses within the microstructure. In this video, designed for beginning materials science undergraduates, we’ll break down the mechanism behind martensite formation and explore how the twinned microstructure can be manipulated to create unique families of shape-memory metals. These fascinating materials have the ability to "remember" and return to their original shape after being deformed. With applications ranging from biomedical stents to the seemingly magical spoons in magic shows, shape-memory alloys have proven to be both practical and mesmerizing.