A display device comprises a source 1 of light of a first polarization, a source of light of a second polarization different from the first polarization, an optical system arranged to image the light emitted by the light sources through a spatial light modulator (SLM) to produce an image of the source of light of the first polarization at a first viewing zone and an image of the second source of light at a second viewing zone, the SLM including a plurality of picture elements arranged to modulate the light emitted by the sources of light, and a plurality of polarization adjusting means each being optically aligned with at least one respective picture element, the polarization adjusting means comprising a first group arranged to permit the transmission of light of the first polarization and substantially prevent transmission of light of the second polarization, and a second group arranged to permit the transmission of light of the second polarization and substantially prevent transmission of light of the first polarization such that the image on the SLM which can be viewed from the first viewing zone is that of the picture elements optically aligned with the polarization adjusting means of the first group and the image which can be viewed from the second viewing zone is that of the picture elements optically aligned with the polarization adjusting means of the second group. The polarization adjusting means may comprise an array of polarizing elements 5a, 5b, or alternatively may comprise an array of wave plates 33. The optical system may comprise a lens 3 or array of lenses provided between the light sources 1, 2 and the SLM 4. A spatial light modulator which may be used in 3D displays of stereoscopic or autostereoscopic type comprises substrates (19, 21) between which is disposed a liquid crystal layer (20). The layer comprises two sets of pixels (12, 13) for displaying left and right eye images. A pixellated polarisation adjustor (31, 32; 33, 34) is disposed between one of the substrates (21) and the liquid crystal layer (20) so as to minimise parallax effects. The pixels (12, 13) of the liquid crystal layer (20) are operated in the same mode i.e. all normally black or all normally white.