"The trick is to use metamaterial, a complex hybrid structure of metal and insulator that makes light move around an object like air flowing over an airplane wing. In a process called refraction, these materials interact with light in such a way that it travels faster through the metamaterial than it does through a vacuum, the famed c in Einstein’s special theory of relativity. Properly tuned, the light emerges from the shield as if there were no object present. But unfortunately for would-be spies, it’s very difficult to make cloaking devices that work on more than one wavelength of light at a time."
Pretty cool, huh?