This Working Paper is based on two research reports that were the outcome of the research carried out by the team of the Universite Libre de Bruxelles within the FP7 project SURVEILLE. Such research focused on the use of surveillance technologies for the prevention, investigation, and prosecution of serious crime. Taken together, the two reports developed a comparative analysis of a number of surveillance technologies and techniques used at different stages of the criminal procedure within selected national jurisdictions. The first project deliverable, finalised in October 2012 and entitled “The use of surveillance technologies for the prevention and investigation of serious crime” (D4.1), addressed the use of the interception of telecommunications and video-surveillance in three countries, namely France, Italy and the United Kingdom. The second deliverable, finalised in April 2013 and entitled “Comparative law paper on data retention regulation on a sample of EU Member States” (D4.3), examined the rules governing the retention of data by telecommunications companies and internet service providers for criminal justice purposes in nine countries (i.e. Belgium, France, Germany, Italy, the Netherlands, Poland, Romania, Spain and the United Kingdom). The two reports test the existence of what the authors call a double shift: the means at the disposal of competent national authorities (intelligence services and law enforcement agencies) in the fight against serious crime are evolving in such a way that the share of tasks and competences is now increasingly blurred. The fundamental rights dimension was the normative background of the legal dimensions of the SURVEILLE project as a whole, and thus also of the present work. The impact of evolving trends in the use of surveillance upon the right to privacy and the right to the protection of personal data are at the core of this research undertaking. The authors wish to highlight that legislation is changing very quickly in this domain both at the national level and at the EU level. In particular, the January 2015 attacks in Paris against Charlie Hebdo, the February 2015 attacks in Copenhagen and the increasing threat resulting from the foreign fighters phenomenon are significantly challenging the effectiveness of means used by States to prevent, investigate, detect and prosecute terrorist offences. Recent legislative developments deepen the blur between the tasks and functions of intelligence services and law enforcement agencies as well as the blur between administrative and criminal law measures. Furthermore, with the ruling by the Court of Justice of the European Union on 8 April 2014 in the Digital Rights Ireland case -- partially reaffirmed in Schrems, EU Member States together with EU institutions have to rethink the legal framework concerning the use of surveillance technologies and techniques in order to ensure a coherent relationship between on the one hand safeguarding the right to privacy and the protection of personal data, and on the other hand developing effective means to prevent, investigate, detect and prosecute serious crime. Despite the fact that the two papers were written at least two years ago, the information remains largely up to date. These papers analyse a trend that has been occurring for some years and that is not over yet: a massive use of surveillance technologies and techniques by an increasing number of competent authorities leading to an exponential gathering of information by EU Member States aiming to fight more effectively against serious crime -- often at the expense of fundamental rights.