The ultimate issue is the core question the judge or jury must decide, for example, the credibility of witnesses. Expert witnesses should be able to give evidence on the ultimate issue before the court, balanced by an appropriate system for testing the quality of expert evidence and increased accountability for expert witnesses. The ultimate issue rule, however, holds that expert witnesses should not give evidence on the ultimate issue, since litigants are entitled to have their disputes decided by a judge or jury rather than by experts. Some contend that expert witnesses undermine the self-esteem of judges and that concern about the cost and duration of litigation mitigates against the use of expert witnesses. Further, lawyers are often reluctant to use the probability statements of scientists as evidence in court. If expert witnesses are employed, courts should decide whom and which disciplines are to be acknowledged as experts. Courts can take several steps to manage the use of expert witnesses: (1) expert evidence should be tendered whenever it may reduce the likelihood of a decision error; (2) the minimum standard for giving expert evidence should be understood; (3) protocols related to expert witnesses should encourage the use of probability statements; (4) implications of decision theory and research should be considered in expert evidence; (5) lawyer and court needs for efficiency and economy should be recognized by expert witnesses; (6) experts should assure that lawyers understand their expertise and its limits; (7) experts should recognize differences between fact and opinion; and (8) expert witnesses should be accountable for what they say to courts. 48 references