The search for an artificial material that would reveal a negative index of refraction at the end of 20th century gave rise to a new field of research called metamaterials. A fundamental feature of metamaterials, a key result of the evolution of metamaterials as a technological gain and as a field of physics, is that their apparently fundamental microscopic properties can be controlled by manipulation of their mesoscopic and macroscopic structure. As a result, the new artificial properties arise, not found in nature before. One such example is the invisibility cloak which guides the electromagnetic waves around the cloaked object in such a manner that the object appears as the empty space to an observer. In order to answer the question in the title, we first demonstrate a way to achieve the desired negative refractive index materials by manipulation of their structure. Relying on the form invariance of Maxwell’s equations under coordinate transformations, we introduce the optical transformation theory which relates the effect of invisibility to the structure of material on supramicroscopic length scales. Optical transformation and metamaterials enable a unique sort of manipulation of electromagnetic waves, the full application potential of which in technology is yet to be accomplished.