The expansive metamaterial concept was developed in 1999 by Rodger Walser, then at the University of Texas in Austin, who suggested that carefully constructed composite materials could achieve physical properties well beyond their constituent components. The idea was not without precedent: Fiber composites—mixtures of carbon or glass fiber and polymers—had existed for decades prior, and were widely used for creating strong yet lightweight structures. Still, Walser and many others believed there was much more to the concept that had not been fully exploited, especially in areas outside of structural engineering. Indeed, as the metamaterials community grew and started avidly exploring the concept, a wealth of new physical paradigms and engineering approaches were quickly discovered. So profound were these discoveries that some of our most basic physical concepts were challenged. In fact, the advent of metamaterials prompted a re-examination of underlying concepts in the field of optics as well as in many other fields. To this day, the metamaterials concept continues to inspire and influence thought across many disciplines of science and engineering.