Among the unusual transport properties predicted for disordered materials is the Anderson localization(1) phenomenon, This is a disorder-induced phase transition in the electron-transport behaviour from the classical diffusion regime, in which the well-known Ohm’s law holds, to a localized state in which the material behaves as an insulator, The effect finds its origin in the interference of electrons that have undergone multiple scattering by defects in the solid(2-10), A similar phenomenon is anticipated for multiple scattering of electromagnetic waves, but with one important simplification : unlike electrons, photons do not interact with one another. This makes transport of photons in disordered materials an ideal model system in which to study Anderson localization(10-17). Here we report direct experimental evidence for Anderson localization of light In optical experiments performed on very strongly scattering semiconductor powders.