An examination of the sanity presumption can produce understanding on two levels: (1) on a practical level and (2) as a reflection of society's values. Historically, the most commonly offered explanation for the presumption is that, ordinarily, people are of sound mind. Because sanity is the normal condition of the human mind, a given individual drawn into the criminal system is more likely than not to conform to this mental condition. However, the article suggested that this justification is false. The early trend toward greater leniency and receptiveness to the insanity defense culminated in the 1843 decision in the Daniel M'Naughten case. Public objection to this ruling led to a demand for specific criteria for determining insanity. The continued validation of the M'Naughten presumption deserves careful attention today. The article argues that the success or failure of the insanity defense in a particular case and as an instrument of social policy may, in large part, depend on the existence and role of the presumption of sanity. At present, the presumption is justified either as a matter of common sense or as a matter of procedural convenience. Because threat to the public safety is no longer an issue concerning such persons, a presumption sanity makes no more sense than a presumption of guilt. In current practice, the presumption continues to operate until the defendant has persuaded the jury of its inapplicability. This burden of proof cannot be justified in terms of the presumption of sanity. In addition, the burden of production may not be placed on a defendant whose insanity assertions would negate a constitutionally essential element of the charged offense. For these reasons, the continued evidentiary role of the presumption cannot be tolerated. Finally, it is suggested that the presumption of sanity is but a part of a larger network of policy determinations that govern the efficary of the insanity defense. The article includes 317 footnotes.