This article provides a critical analysis of immigration detention regime under European Union (EU) law. It assesses the relevant provisions of the EU Returns Directive and their domestic implementation in several EU states against the underlying requirement for any deprivation of liberty not to amount to arbitrary detention. Three elements embodied in this requirement are highlighted: the exceptional nature of pre-removal detention, its use as a last resort, and its shortest possible length. The article argues that by using broad terms, the EU Returns Directive falls short of providing for strong safeguards against arbitrary immigration detention. In fact, pre-removal detention imposed in an automatic manner and for lengthy periods is not necessarily incompatible with the EU Returns Directive. Moreover, national authorities may actually use some of its provisions to justify more stringent measures.