A substantial body of research bears directly on the perception, memory, and recall of complex events of the kind involved in eyewitness testimony. This research indicates that eyewitness testimony can be viewed as a three-stage process. During the first stage--acquisition--an event is perceived and information about it is initially stored in memory. In the second stage--retention--information is resident in memory. In the final stage--retrieval--memory is searched and pertinent information is retrieved and communicated. A common belief is that information, once acquired by the memory system, is unchangeable, and that errors in memory result either from an inability to find stored information or from errors made during the original perception of the event. The evidence examined supports the alternative position that stored information is highly malleable and subject to change and distortion by such events as misleading questions and overheard conversation occurring during the retention stage. Evidence presented indicates that once memory for some event has been distorted by intervening events, the information acquired during perception of the original event may never be recovered. The impact of eyewitness testimony on the legal system is examined, and the enormous credibility that eyewitness testimony is likely to have in jury trials is indicated. Common mistaken beliefs about eyewitness testimony are presented, and the degree to which such beliefs produce erroneous decisions is determined. The legal status of eyewitness testimony and the role of expert testimony on the matter is delineated. The final chapter provides a detailed account of a murder case in which eyewitness testimony played a key role. The transcript of the expert testimony provided in the case is appended, and about 200 references are listed. An index is also provided. (Author abstract modified)