This doctoral thesis aims to study the legal system of the European Union (EU) with a focus on the EU's responsibility in asylum policy in relation to the principle of non-refoulement. The principle of non-refoulement, as widely recognised as an absolute norm, prohibits the transfer of people to countries considered unsafe. However, its correct application in the EU seems to be circumvented by the principle of mutual trust and the concept of safe country. Therefore, this research, by analysing legal texts, case law and policy documents, critically examines how these two concepts attempt and sometimes succeed in circumventing the principle of non-refoulement. The examination conducted shows a considerable discrepancy between the theoretical construct of the non-refoulement principle and its application in practice within EU Member States. Mutual trust often results in infringements of the rights of asylum seekers when they are transferred from one EU country to another, and at the same time, the safe country concept, which is open to political interpretation, also most frequently leads to these infringements. This thesis, by illustrating the practical difficulties of protecting the principle of non-refoulement and how some policy choices are not in line with the EU's human rights obligations, contributes to the debate in the EU on asylum and refugees.