Abstract Circular dichroism and optical activity are well known manifestations of optical activity. In recent years several novel types of optical activity have been observed. An achiral system bathed in an intense beam of circularly polarized light shows chiral behaviour which can be detected as circular dichroism or optical rotation. In another type of induced circular dichroism, a chiral solvent is used to induce chirality. Theories of natural and induced optical activity are reviewed within a unified framework using quantum electrodynamics. Chiral discrimination refers to the dependence of the interaction energy of two chiral molecules upon the relative handedness of the two species. The inter-molecular interaction can be modified by the presence of an intense radiation field. Theories of discriminatory interactions are discussed within a quantum-electrodynamical viewpoint.