This article examines how French law defines and deals with undesirable and unreturnable migrants in a time when the political context is particularly tense. “Undesirability” refers to the situation of migrants who are subjected to a deportation measure as they are deemed a threat to public policy, while “unreturnability” refers to migrants who are subject to a deportation measure that cannot be enforced. I will discuss the way French authorities assess the undesirability of non-nationals, and demonstrate that they enjoy a wide degree of discretion in this respect. I will then propose a typology of the reasons for unreturnability, which are numerous and not necessarily connected to the behaviour of the migrant that is subject to the deportation measure. Finally and most importantly, I will focus on the tools French law provides for the management of undesirable and unreturnable migrants. In this respect, I will demonstrate that these individuals are either subject to de facto unlimited restrictions to liberty, or left to their own devices with a precarious liberty that comes with lowered rights. We will see that ultimately, they find themselves trapped between legal uncertainty and legal limbo, thus they are “expelled” from the rule of law.