A polarising security element for polarising light of a predetermined wavelength is provided which includes a first dielectric material (30) having a refractive index nb, and at least one polarising region of mutually parallel segments (34) of a second material having a refractive index np which is different to nb, the second material being a dielectric or conducting material. The segments (34) of the second material are in contact with the first material (30) and the segments (34) have a width and/or an average spacing which is less than a predetermined range of wavelengths. A method of manufacturing such a security element is also provided in which a relief structure is embossed in the layer of the first dielectric material (30), the relief structure including a plurality of mutually parallel peaks and troughs (32,33), and the second layer of dielectric or conducting material is applied on the relief structure, preferably by printing, to form the at least one polarising region of mutually parallel segments (34).