Perpetual copyright refers to a copyright which does not expire. It is highly uncommon, as the current laws of all countries with copyright statutes set a standard limit on the duration, based either on the date of creation/publication, or on the date of the creator's death. (See List of countries' copyright length.) Exceptions have sometimes been made, however, for unpublished works. Usually, special legislation is required, granting a perpetual copyright to a specific work.