This Liberty and Security working paper seeks to understand the reasons behind the considerable complications facing the project to develop a new, second generation version of the Schengen Information System (SIS II). Despite the centrality of this large-scale EU database for immigration and border control purposes and the increasing prioritisation of security technologies within the EU’s internal security strategy, the project has encountered substantial delays, an escalating budget, political crises and criticisms of the new system’s potential impact on fundamental rights.