This book focuses on legislative frameworks for data access investigative measures in the EU, and their legal conflicts with data protection law. It identifies four data access investigative measures developed by EU law: access to passenger name records, access to financial data, access to electronic communications and access to e-evidence. The security objectives pursued by data access investigative measures conflict with the fundamental right to personal data protection guaranteed by Article 8 of the Charter of Fundamental Rights of the EU. While there is a lot of case law of the Court of Justice of the EU dedicated to data access investigative measures, the Court is struggling with finding a correct and workable solution for the conflict. The book finds the best available method to strike the right balance and solve the apparent legal conflict, while positioning the outdated cliché on 'privacy v. security' in a proper empirical and theoretical framework.