Throughout human history, improvements in the structure of metals have been essential to the sharpness of swords and the strength of steel girders. Now we’d like to produce turbine blades and propellers with optimal shapes and long useable lifetimes through 3-D printing. This is a fundamentally new way of manufacturing things, building them up layer by layer rather than by carving or molding materials. Also known as “additive manufacturing,” this method will allow us to create exceptionally complex metal parts on demand, make faster, lighter vehicles, prototype new technologies and even build habitats on distant planets. But to make it work, the structure of the printed metal has to be reliably strong and uniform at the microscopic and even the atomic scale. Achieving this high level of precision and control will require a solid understanding of exactly what is happening to the microstructure of a printed part as it is being created. At SLAC, we have developed tools for looking beneath the surface of metal additive manufacturing, understanding the physics involved and controlling this physics to create the metal components of the future.