The European Union's Directive 2008/115/EC and Member States implementation thereof, subject Third Country Nationals awaiting for return/removal from the European Union, and its subgroup of non-returnable Third Country Nationals, to conditions of cooperation in order to access human rights. This creates a tension in relation to the principle of non-discrimination in that all individuals, regardless of migration status, are to access their rights. Nevertheless, the concept of cooperation is about to be expanded in the European Union's regulations on migration. This thesis assesses the prevailing legal understandings of the concept, within the European Union and across its Member States, against the principle of non-discrimination. The conclusion of how these understandings fare is that it depends. It depends on what method of legal interpretation is used when interpreting the concept and against which general interest of the European Union it is being compared against; that of the prerogative to exercise border control or that of protecting fundamental rights.