The criminal process is, to a large extent, an investigative one, existing to prepare cases for effective trial. To this end, authorities are given powers enabling them to gather evidence. But these powers can infringe numerous interests, some relating to the workings of the process itself, in addition to external ones, such as liberty, privacy, freedom from humiliation, and bodily integrity. This chapter examines how the gathering of evidence is and should be affected by these concerns and covers powers and practices in relation to the investigation of crime and the gathering of evidence. It discusses stop and search, surveillance, eyewitness identification evidence, voice identification, forensic and biometric samples, and the privilege against self-incrimination.