Recent years have been marked by a growing demand of personal data for public security purposes. Access and protection of those data are climbing the transatlantic political agenda. They have raised tensions and fostered forms of cooperation. The possible conclusion of an international binding agreement on a common transatlantic framework on data protection would be a further and crucial step ahead. The scope of this study is to pave the way for launching a parliamentary debate on those issues. Therefore, it aims at providing a comparative analysis of the EU and US legislation concerning the protection of personal data collected for public security purposes. It also discusses some of the main challenges posed by new technologies as well as analyses the most relevant cases-studies of transatlantic data exchange. Finally, it takes into consideration the published outcomes of the work of the High Level Contact Group.