In 2015/16, Europe faced the largest inflow of refugees since World War II. This inflow highlighted systemic deficiencies in EU asylum co-operation which provoked a state of crisis. Together with the Eurozone crisis, this crisis has the potential to seriously damage the overall project of EU integration. The goal of this Special Issue is to provide a first systematic assessment of the crisis, applying and further developing key theoretical approaches to the sequence of events. In empirical terms, we advance original empirical evidence in order to deepen our understanding of the crisis and how it has been managed. In theoretical terms, we seek to (re)assess the usefulness and limitations of some important theoretical perspectives to European integration at a critical juncture of the EU's history. After presenting the sequence of events and assessing the EU's crisis response, the introduction will summarize our main findings and present avenues for further research.