This chapter examines the relationship between EU immigration law and national criminal law. By focusing on the jurisprudence of the Luxembourg Court on the Return Directive, it analyses three seminal judgments, El Dridi, Achughbabian and Sagor, and explores the reactions at the national level in the aftermath of their release. The examination of these cases reveals the important limits placed by the Court to Member States’ power to impose criminal sanctions (both custodial and financial) on third-country nationals for their breaches of domestic immigration law provisions. On the basis of the case law, while the return process is ongoing in Member States an irregular migrant may not be placed into custody, as this is liable to jeopardize the attainment of the Directive. Even after such process has failed, a custodial sentence may only be imposed if the failure of the return procedure may be pinned down on them.