http://wired.com/news/technology/0,70997-0.html

[John Pendry, a physicist at the Imperial College London] and his co-authors propose using metamaterials because they can be tuned to bend electromagnetic radiation — radio waves and visible light, for example — in any direction.

A cloak made of those materials, with a structure designed down to the submicroscopic scale, would neither reflect light nor cast a shadow.

Instead, like a river streaming around a smooth boulder, light and all other forms of electromagnetic radiation would strike the cloak and simply flow around it, continuing on as if it never bumped up against an obstacle. That would give an onlooker the apparent ability to peer right through the cloak, with everything tucked inside concealed from view.