Also known as: ex-post-facto · ex post facto law · retroactive law
Written by attorneys · grounded in primary & secondary sources — see below
A constitutional prohibition that bars legislatures from enacting criminal laws making conduct criminal after the fact or increasing punishment for past acts. The prohibition protects fair notice by ensuring individuals may rely on existing law when ordering their affairs. It applies to statutes that retroactively alter the legal consequences of completed conduct in a punitive manner.
Apex Telecom used a foreign network vendor in prior years when that use was lawful. Congress later enacts a statute making the past use a federal offense and imposing mandatory punitive security penalties calculated per year of prior use. Apex Telecom challenges the statute on constitutional grounds.
Eileen Epstein's alleged conduct occurred years earlier and the statute of limitations had already expired. The legislature then enacts a statute extending the limitations period and reviving the expired claim. Prosecutors bring charges against her under the new extension.
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Titan Industries emitted carbon in years when no output ceilings existed. Congress later passes a statute making those prior emissions a federal crime and referring the company for prosecution. Titan moves to dismiss the charges on constitutional grounds.
Ezra Eastman is tried for a crime committed when state law required a twelve-person jury. The legislature reduces the required jury size to eight before trial. The court applies the new size to Eastman's case over his objection.
Eastern Electric made political contributions under rules in effect at the time. Congress later enacts stricter limits and applies them retroactively to impose penalties on the prior contributions. The company challenges the retroactive application.
Emanuel Escobar assisted a terminally ill patient under state law permitting the act when performed. The legislature later bans the conduct and applies the ban to prior assistance. Prosecutors charge Escobar under the new statute.
The clause bars legislatures from enacting criminal laws that retroactively make previously lawful conduct a crime or increase punishment for past acts. It ensures fair notice so individuals may rely on existing law.
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The clause applies only to criminal or punitive laws. Civil measures are outside its scope unless they are so punitive in purpose or effect that they function as punishment.
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Yes. A statute that retroactively revives a time-barred criminal prosecution by extending the limitations period after expiration violates the clause because it reopens the possibility of punishment for past conduct.
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A sentencing law or guideline that increases the punishment for a crime after the crime has been committed violates the ex post facto prohibition.
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The constitutional prohibition applies only to legislative acts. Due process may bar courts from retroactively interpreting criminal law in an unexpected and indefensible manner.
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…a measure was "necessary and proper" to the discharge of its substantive legislative authority, pass a bill of attainder or ex post facto law contrary to the prohibitions contained in § 9 of Art. I. No more may it vest in itself, or in its officers, the authority to appoint officers of the United States when the Appointments…