This article explores whether authors can dedicate their copyright to the public domain. Such dedications are becoming increasingly relevant as authors now see the expansion of the public domain as value in itself. This is facilitated by organisations providing pro forma documents for dedicating works to the public domain. However, there has been no real consideration of what, if any, legal effect a dedication to the public might have. This article suggests that such dedications are no more than copyright licences which, in English and US law at least, can be revoked at will. This means that users of such works must rely on estoppel alone to enforce any dedication to the public domain.