The point of the book is to elucidate the changing policing zoom, from a focus on the local, via a centralisation and nationalisation process, and towards the more supranational current situation, that may first be seen in the Norwegian context as of the Schengen negotiations, and to consider how and to which extent this change has affected Norwegian sovereignty in different perspectives. To understand the Union’s move towards more ‘integrated’ policing instruments, it is necessary to give an overview of the cooperation development in the Union. There have been two main trajectories of the development of police cooperation within the EU proper: the TREVI cooperation, leading to Europol, and the Schengen police cooperation, leading to the Schengen Convention that was later incorporated into EU law. Both are elaborated on in depth below, including the different available police measures, included those that have been developed in later agreements. Prior to that, the way these two first cooperation mechanisms were evolved, needs some explanation. The Europol track is the main focus in this chapter, while Schengen is developed together with the Norwegian relationship to it, in Chapter 6.