An intriguing proposition in the study of the EU’s area of Police and Judicial Cooperation Criminal Matters (PJCCM) has been that Member States’ (governments) institutional choices in this policy area reflect motives to enhance their autonomy/discretion vis-à-vis domestic and/or supranational actors. According to this argument, by cooperating in an intergovernmental setting governments can circumvent domestic institutional constraints, while at the same time keeping the influence of supranational actors at bay. What is the empirical basis of such claims? Do governments’ institutional preferences indeed reflect strategic attempts at increasing their autonomy vis-à-vis domestic actors in law enforcement policies, as suggested by some authors? Moreover, once institutional rules have been put in place, are governments able to use these rules so as to circumvent EU level constraints? To answer these questions this thesis examined institutional preferences and strategies of governments at Treaty negotiations and in the day-to-day policy-making process in the policy area of PJCCM. In the first part of the thesis, the alleged connection between institutional constraints governments face in their domestic arenas and their respective institutional preferences at Treaty negotiations was tested. In a second part, strategic interactions between governments in the EU Council and the European Commission with respect to institutional rules in the legislative process in PJCCM were examined. The empirical results of both parts suggest that while only a moderate connection between domestic constraints and governments’ institutional preference at Treaty negotiations could be identified, there seems to be a systematic relation between rising EU level constraints and strategic institutional choices of actors that reflect motives for autonomy/discretion. The driving factors behind these day-to-day strategic interactions are the ambiguity of and interstitial changes to institutional rules. More specifically, this thesis shows how ambiguous rules over EU competences in PJCCM and changes to these rules via rulings of the Court of Justice lead actors to deploy litigation strategies (Commission), as well as legislative pre-emption strategies (Member States). Furthermore, these conflicts continue to also characterize the policy-making process in PJCCM after formal institutional reforms (post-Lisbon). Going forward, this thesis suggests that more, rather than less, of these strategic interactions will take place in the near future.