Abstract: The present invention relates to novel entangled-photon microscopy, spectroscopy and display systems. The systems include a source of light in the form of twin or multiple entangled-photon beams. The systems also include optical components that direct the twin or multiple entangled-photon beams towards a target material. The target material includes emission or indicator means responsive to an energy, which approximately equals the sum of the energies of the entangled photons. The systems may further include imaging means that is sensitive to the response of the target material. The present invention also relates to novel correlated-photon microscopy, spectroscopy and display systems. The present invention further relates to methods of correlated-photon microscopy in which a pump beam of photons is provided. A portion of the pump beam is split into a first beam and a second beam, the beams having corresponding correlated photons.