The detention of migrants who have not committed a crime is one of the most disturbing contemporary practices from the point of view of human rights (Costello 2015). Administrative detention of asylum-seekers poses an additional problem: it causes an independent deterioration of the mental health of people who are (potentially) already highly traumatised (Filges et al. 2015). The intention of this book is to systematise in a comprehensive manner the obligations that States owe to detained asylum-seekers under the European Convention on Human Rights (ECHR).