This final chapter considers the investigative powers that the police use. It includes an examination of digital evidence, and notes that often this is what poses challenges to the police. Gaining possession of the device in order to investigate it can be a real challenge, particularly when the offender or the victim’s computer is outside of the jurisdiction. Even when both parties are within the same country, the sheer amount of material that is stored on electronic devices can pose real challenges to law enforcement. The chapter then turns its attention to communications data. This is an extremely controversial area of the law, and it is where the police and security services can gather data in respect of the use of the internet, device or telephone. While the content of a communication cannot be gathered (as that constitutes an illegal interception), it does include the who, what and how. This allows the police or other agencies to build up a picture of what sites are being accessed, or who a suspect is talking to. The issue of bulk data collection – where large numbers of people’s data are gathered – is also considered in this chapter. There have been many challenges to this area, and the courts have considered some of the powers to breach human rights. The principal challenges to the investigatory power’s regime are considered, and an analysis is made of where the courts draw the line. The final section of the chapter looks at online surveillance, including OpenSource Intelligence. This is how law enforcement can use publicly available information such as websites and social media postings to gather intelligence on a group or individual’s online dealings. The second aspect of surveillance that is considered is the use of Covert Human Intelligence Sources (CHIS), who will act as undercover agents to talk to people online. This is particularly common in respect of the sexual solicitation of children, and the chapter notes how the courts have reacted to this.