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Materials that can bend light in the opposite direction to normal ('left-handed'materials) reverse the way in which refraction usually works—this negative refractive index is due to simultaneously negative permeability and permittivity 1, 2, 3. Here we demonstrate negative refraction of electromagnetic waves in a two-dimensional dielectric photonic crystal that has a periodically modulated positive permittivity and a permeability of unity 4, 5, 6. This experimental verification of negative refraction is a step towards the realization of a'superlens' that will be able to focus features smaller than the wavelength of light.