Abstract: An optical data storage medium comprises a substrate layer, a recording medium and an optional protective layer. The substrate layer supports the recording medium. The recording medium comprises a polymer having stable amorphous and crystalline states under human operating conditions which states have different optical properties. The recording medium is optionally covered and protected by a protective layer. The substrate, recording medium and protective layer can be formed from the same or different polymers. The data is stored by exposing the recording medium to patterned infra-red radiation. The radiation can be patterned by a mask, movement of the radiation beam or by other means to imprint the data on the recording medium.