Foreword Detention of a person constitutes a major interference with personal liberty. Any deprivation of liberty must therefore respect the safeguards which have been established to prevent unlawful and arbitrary detention. This is also the case when detention is resorted to in order to facilitate the removal of irregular migrants. Thus, while pre-removal detention is not in itself a violation of human rights law, it can become so. This would, for instance, be the case when the grounds justifying detention are not laid down in national legislation in a clear and exhaustive manner, or when the detention was not carried out in compliance with the procedural or substantive rules as stipulated by law. Detention of irregular migrants in return procedures has been subject to heated discussions during the negotiations of the Return Directive. This report tries to deconstruct the various elements of the right to liberty and the prohibition of arbitrary detention. It presents for each of those elements an overview of applicable international law standards, as well as state practice with the aim of facilitating an objective discussion on these issues. This report has to be seen against the background of the work by the European Union Agency for Fundamental Rights (FRA) in the context of the Contact Committee of the Return Directive, to which the Agency has been invited to participate in meetings by the Commission. The FRA shared preliminary considerations on selected fundamental rights issues covered by the Return Directive with members of the Contact Committee in September 2009. A draft version of this report has also been shared with the Committee members for comments which have been taken into account when drafting this report. It is thus based on information up until September 2010. Member States are required to transpose the Return Directive by the end of 2010. With its engagement with the Contact Committee and through this report, the FRA hopes to assist Member States in dealing with the fundamental rights challenges raised by the complexity of the subject. Morten Kjaerum Director