LEGAL BACKGROUND People on the move are particularly vulnerable to deprivation of liberty, which is often used by states to discourage irregular migration. Administrative detention - which results in individuals being detained in special facilities rather than in judicial prisons - is commonly used for detaining third country nationals. The purpose of administrative detention is to facilitate other measures, such as deportation or the asylum procedure.. There are also many instances of administrative detention based on other grounds, such as public security. This research focuses on the administrative detention of two legally defined groups - third country nationals, detained in view of removal, and applicants of international protection - detained in PRDCs in Greece. Basic principles & legal structures for the detention of applicants of international protection Detention is a severe interference with the basic human right to liberty and as such can only be applied in very specific circumstances and conditions. The European framework and the Greek law provide that asylum seekers can not be detained “for the sole reason that he or she is an applicant for international protection or that he or she has entered the country illegally and/or stays in the country without proper documentation.”[12] According to the Reception Conditions Directive (RCD)[13] and the European Court of Justice (ECJ), detention of asylum seekers can only be implemented as an exceptional measure, in clearly defined circumstances,[14] “when it is determined to be necessary, reasonable and proportionate to a legitimate purpose”.[15] In transposing the RCD, Greek law sets out an exhaustive list of reasons for which asylum seekers can be detained[16] in order to comply with the principles of necessity and proportionality.[17] However, the deprivation of liberty is possible only if other less coercive alternative measures to detention cannot be applied effectively, after an individual assessment.[18] Despite the obligation by law, the application of alternative measures are in Greece neither examined nor applied in practice[19] and there are serious doubts if the Greek police, as the competent authority to impose detention, is conducting individual assessments.[20] Finally, due diligence is required for the execution of administrative procedures[21] and asylum seekers can only be detained for as long as it is absolutely necessary and while the grounds for their detention are applicable. In Greece, the initial period is 50 days which can be extended for another 50 days. The maximum time frame for an asylum seeker to be detained is 18 months[22] and the same time period can be added in view of removal (in case of rejection).[23] 10