The evaluation of testamentary capacity represents a field requiring serious psychiatric consideration. While considerable publicity and work have recently been afforded the problem of criminal responsibility, little can be found in recent psychiatric literature regarding testamentary capacity. There have been some noteworthy exceptions, and Davidson's clear, simple and concise chapter in his recent book(52) is a major contribution.No court or tribunal can set up a standard by which mental capacity may be unerringly tested. No jurist or psychiatrist has indicated a precise point where sanity ceases and insanity begins. Perhaps it would be easier to decide the exact instant when dusk surrenders to darkness.The psychiatrist faces the problem of providing expert testimony based on the application of psychopathology to criteria set by law. These criteria may appear quite ambiguous or they may be satisfied in a manner that the psychiatrist may feel injustice is being done. The psychiatrist may be disconcerted by some of the discourtesies and lack of weight afforded his testimony.The conditions under which testamentary capacity can be contested are fairly limited. The value of having the psychiatrist present at the time the will is being drawn up is important, especially when the premise of lucid interval is to be utilized. In the majority of cases where wills are contested, the psychiatrist rarely has the opportunity to examine the testator and has to depend on the available history. He must obtain facts as best he can and render an honest opinion as to testamentary capacity. The lawyer's duty to his client is to give him the benefit of the best legal ability of which he is capable; so naturally a lawyer, consulting a psychiatrist, will try to present witnesses who primarily favor his side. Progress has been made in many states by the appointing of impartial medical experts for lunacy commissions and cases involving personal injury liability. It would be an important step to have such impartial opinion applied in cases involving testamentary capacity.There is increasing awareness on the part of the legal profession of the real contributions which an understanding of behavioral mechanisms can make toward better conceptualization of the law and its procedures. Psychiatry is the medical specialty which has the closest contact with law. It too is directly concerned with the appropriate regulation of human behavior in a healthy manner. Psychiatry, however, is neither as pragmatic, authoritarian or precise as the law. Although present-day dynamic psychiatry recognizes the vital impact of the unconscious motivation of behavior, law leaves no place for such recognition although it is beginning to take hesitant steps in that direction.