This book provides the first comprehensive doctrinal and comparative study to examine the influence of the fundamental human right to respect for private life on data retention within EU law, specifically communications data and passenger name record data, for the purpose of countering serious crime. First, it is the only academic publication that offers a complete picture of the EU's institutions, not just the Court of Justice of the EU, at work in a legally and politically sensitive field from a variety of perspectives, thereby contributing to a scholarly understanding of topics which tend to attract generalized opinions not based on detailed analysis of law and practice in specific areas. Secondly, this original analysis of EU data retention law casts a spotlight on the real and actual extent of the weight now being given in the mainstreaming of fundamental rights within the EU policymaking process, providing a more complete picture of the role and impact of human rights on this area of law and policymaking. Thirdly, this book is the only work to outline and examine in detail the impact of the tensions and dialogue between the EU and European Convention on Human Rights (ECHR) legal systems within the case law of both courts on data privacy and serious crime. In addition, this book also sets out the implications of the above analysis, and recent landmark jurisprudence on Article 8 ECHR and Articles 7 and 8 of the EU Charter of Fundamental Rights, for new related EU legislation, including Directive 2016/680 on data processing for the purposes of the prevention, investigation, detection or prosecution of criminal offences and relevant provisions of the forthcoming E-Privacy Regulation.