The establishment of an area of "freedom of movement" without border control within the Schengen-area is deemed one of the major achievements of European integration. However, developments since 2015 have shown a renewed salience of internal borders. This is due, on the one hand, to the introduction and maintenance of temporary border control by several member states, which was justified as a response to unauthorised mobilities problematised as "secondary movements". On the other hand, also border-regions adjacent to internal borders have acquired an increased strategic importance. Particularly the European Commission advanced the recommendation to shift towards enhanced (national) border-area police-checks and police cooperation as an alternative to border control. Both the Treaty on the Functioning of the European Union (TFEU) and explicitly the Convention Implementing the Schengen Agreement (CISA) encourage bilateral police cooperation between member states, foreseeing particular measures for countries that share a common border. Various studies conducted in the 1990s engaged with initially informal, and increasingly formalised, forms of cooperation across borderregions. In current times, practices of cross-border police cooperation as well as of migration policing at internal borders constitute a substantial knowledge gap.In this dissertation I examine the intersection of cross-border police cooperation (CBPC) with the control of differential mobility rights within today's EU Area of Freedom, Security and Justice. I conceptualise and analyse CBPC as policing-mobilities in the border-strip. Grounded in empirical fieldwork with police officers, this study fills important research-gaps that persist with regards to a twofold inquiry: a) police cooperation at the scale of border-regions and b) the policing of mobilities at internal Schengen borders. Specifically, this study concentrates on three CBPC instruments: joint police centres or PCCCs, (joint) border-area patrols and bilateral simplified fasttrack readmissions. Some of these were also amongst the "best practices" and alternatives which since 2017 the Commission has recommended to enhance. Beyond findings of analytical relevance, this study allows one to critically engage with the envisaged border-area 'solutions'.In PART I, I place this dissertation at the crossroad of social-science and law within a multidisciplinary field of scholarly engagement. I outline the theoretical framework and methodological approach of a multisited research design. Rather than conducting a research that favours a focus on discourses and laws or on situated practices, I studied both elements and the interdependence between law-as-text and as-practice, aiming to get a grasp of large-scale processes not reducible to one empirical field-locale. In PART II, I draw attention towards the spatial-legal regimes that regulate CBPC and trace their emergence as institutionalised regimes of practices. I argue that they constitute the border-strip as spatial-legal condition of possibility xv...