The topic of the public domain has a long-standing history in Anglo- American copyright law, which can be traced back to at least the Statute of Anne. However, it was in 1981, when David Lange wrote his seminal article on this topic, that there was renewed academic interest in the public domain. A noteworthy feature of these academic commentaries is the commonly held premise that there is, or there has been, a phenomenon of excessive encroachment by IP upon the public domain. What typically underpins these commentaries is the presumption that there are subject matters in the public domain that are, or ought to be, incapable of propertization (“unpropertizable”). Therefore, this article investigates the public domain’s (negative) “non-property” status with the goal of increasing its visibility in UK and EU copyright law amid the risk of such encroachment. It does so by examining the strongest form of “non-property,” namely subject matters in the public domain that are “unpropertizable.” This investigation is structured into four Parts. In Parts II-IV, this article identifies three possible understandings of “unpropertizable” subject matters in UK and EU copyright law. It then examines one means by which encroachment might be facilitated in practice upon these unpropertizable subject matters. This is where there is flexibility in the legal rules that render certain subject matters unpropertizable which might, in practice, allow judges to circumventtheir “unpropertizable” status. In Part V, this article contemplates the implications of its investigation into the public domain’s “non-property” status, with particular focus on recent developments in UK law now that the Retained EU Law (Revocation and Reform) Act 2023 is in force.