The aim of this paper is to question, from the perspective of a principled theory of criminalization, the legitimacy of making irregular immigration a crime. In order to do this, I identify three main ways in which the political decision to introduce a crime of IM may be defended: according to the first, IM is a malum in se the wrongness of which resides in its being a violation of states’ territorial sovereignty; according to the second, IM is a justified (...) malum prohibitum the wrongness of which resides in its being a violation of a justified immigration regulation; according to the third, IM is a malum in se the wrongness of which resides in its harmful consequences for receiving states’ citizens. My thesis is that none of these arguments succeeds in providing us with sufficiently good reasons to justify the use of criminal punishment to enforce the closure of state borders. As regards the first, I argue that it relies on a misleading conception of what is entailed by states’ territorial sovereignty, and that therefore it is unsound as an argument for the state’s right to control immigration. With regard to the second, I argue that, be they legitimate or not, immigration regulations enacted by states cannot provide those would-be immigrants they aim to exclude with content-independent reasons to comply with them; and this is a necessary pre-condition to conclude that IM is a justified malum prohibitum. As regards harm-based approaches, I argue that the notions they rely on are completely unfit as criteria for criminalization. This leads me to the conclusion that, unless other more convincing arguments are provided for, IM should not be criminalized. (shrink)