Amid the recent and unprecedented influx of migrants into the European Union, the functioning of Schengen has been placed under considerable strain, with several member states re-introducing temporary controls on parts of their internal borders. Recent evidence suggests that suspensions of Schengen are associated with economic costs related to trade barriers and traffic delays at border crossing points, among others things. Against this background, the European Parliament commissioned RAND Europe to investigate the economic, social and political costs of non-Schengen, with a particular emphasis on civil liberties and home affairs. This study aims to contribute to discussions about Schengen's sustainability in the light of the migration crisis by identifying the costs of re-introducing border controls between Schengen member states, and by identifying the potential benefits of more concerted action at EU level compared to the lack of such action, or to action by member states on their own. The remit of this study includes both economic costs (such as re-introducing internal border controls) along with wider social and political costs (such as crime, and measures of security and trust). The focus on the latter types of cost reflects the fact that, as well as its economic benefits, Schengen has also been a building block of the EU's Area of Freedom, Security and Justice, and as such has an importance beyond the purely economic.