All fusion devices generate large amounts of data, which must remain accessible throughout and beyond the lifetime of the device. This need for long-term data preservation creates major software and hardware challenges. Issues surrounding long-term data preservation will be discussed, and the main challenges in data curation will be outlined. The paper will then review the approaches taken at JET to ensure accessibility of all of JET's data over almost three decades. Using the JET experience and the wider context, the paper will then suggest how new experiments should plan for the long-term preservation of their data.