Chapter 6 looks at how, in democratic societies, the regimes of data collection for the purposes of national security and law enforcement have traditionally been strictly separated. Yet, in the last two decades, complex challenges such as organised crime and terrorism have blurred the border between them, raising concerns about the use of data collected by intelligence agencies as evidence in criminal investigations. The chapter examines issues related to exchange of information between national security and criminal justice domains. It discusses problems associated with the inherent imbalance in aims, functions and safeguards between the two regimes. While considering the exchange of data between intelligence agencies and law enforcement inevitable, the chapter argues that the differences between the regimes create a danger of using national security frameworks to circumvent strict safeguards established in criminal procedure law. It suggests that robust safeguards and measures for accountability and oversight must become an integral part of frameworks that enable and facilitate data flows from the national security domain to criminal investigations.