The roles assigned to the forensic psychologists are discussed as (1) the experimental role, which involved the application of established experimental data to the events of a particular case to produce an authoritative interpretation of what transpired; (2) the clinical role, which focuses primarily on a scientific determination of the defendant's mental state; (3) the actuary role, which involves providing information on the probabilities of certain events occurring alone or in conjunction with other events; and (4) as adviser, which involves informing the court on a scientific matter which requires explanation and elaboration. The second paper on the psychologist as expert witness advises that the effectiveness of the testimony of a forensic psychologist depends greatly upon the existence of applied research findings relevant to the legal issue being considered in court. It is recommended that the legal community become involved in seeking financial support for such research. The paper that considers the place of mental elements in psychology and law discusses the perspective of behaviorist theory regarding this issue. Behavorist psychology emphasizes the importance of examining the pattern of environmental influences impacting a defendant's outlook and behavior in the particular circumstances of the offense more than autonomous mental attitudes, which are difficult to determine. The emphasis under such an approach would be upon the dangerousness of the conditioned behavior more than the culpability determined by the defendant's mental state. Psychological factors influencing the accuracy of eyewitness observations are considered in the concluding paper. References accompany each presentation.