The experimental psychologist qualifies as an expert on the basis of the formal academic training required to enter the profession: an undergraduate degree which includes a psychology major and at least one postgraduate year. Although experimental psychologists qualify as expert witnesses, they are seldom used by the courts because of the generally held view that judgments about human behavior involve mere common sense and an average degree of introspection. Empirical evidence indicates, however, that 'common-sense' and introspective judgments about human behavior and capacities are unreliable. The findings of experimental psychology can contribute to the increased effectiveness of judicial proceedings by providing criteria for the type of testimony that is reliable, guidelines for suspect identification procedures, and parameters for courtroom procedures. Experimental studies that have analyzed the operation of human memory yield results that should be taken into account when judging the credibility of witness testimony, and empirical studies have also identified the circumstances under which suspects are most likely to be correctly identified by witnesses. Experimental studies also yield evidence that the courtroom procedures that permit rulings on evidence admissibility in the presence of a jury and allow the jury to observe the physical characteristics and demeanor of the witness and defendant undermine the objectivity of decisionmaking based on the admissible evidence. The experimental psychologist can be helpful as an expert witness by advising the court of pertinent research findings, providing the court with the details on the competency of a particular person, evaluating the reliability of certain evidence, and rendering an expert decision on the likelihood of the occurrence of certain behavior. Thirty-four references are provided.