The memories of eyewitnesses play a central role in many police investigations and any subsequent legal decision making. Unfortunately, eyewitness memories are not infallible. This chapter presents an overview of areas where programmatic research has explored factors contributing to witness unreliability and suggested ways of improving the quality of eyewitness evidence. The chapter's organization loosely parallels the sequence experienced by witnesses from the time of crime commission, through their involvement in a police investigation, to that in any subsequent trial. During the time between the event and the witness being interviewed by police, a number of factors can shape the memory reports of the witness. As well as providing details about the event and offender, witnesses may also be asked to view a formal identification parade. Scientific research on eyewitness memory issues has grown steadily in the last twenty to thirty years.