Also known as: ex post facto laws · ex-post facto law · ex-post-facto law · retroactive law · ex post facto
Written by attorneys · grounded in primary & secondary sources — see below
A legislative enactment that retroactively alters the criminal law in a manner prejudicial to the accused. Such a law either criminalizes conduct lawful when performed, increases punishment for a completed offense, or changes evidentiary rules to the defendant's disadvantage.
Emily Ellis completed a series of financial transactions in 2022 that carried a maximum five-year sentence under then-existing state law. In 2024 the legislature raised the maximum to ten years and directed the new ceiling to apply to all prior conduct. When Emily is sentenced under the higher range, the court must reject the enhanced term because the statute operates retroactively to increase punishment for completed acts.
Ewan Eckhart's alleged securities violation occurred in 2015 and the five-year limitations period expired in 2020. Congress later enacted a statute reviving all such expired prosecutions and extending the period to eight years. When prosecutors charge Ewan under the revived statute, the court must dismiss because the law retroactively reopens punishment for conduct whose prosecution had already become impossible.
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Ella Emerson emitted carbon levels in 2018 that were lawful under existing federal rules. A 2023 statute makes exceeding newly adopted ceilings a federal crime for any prior year and refers Ella for prosecution. The court must dismiss the charges because the statute retroactively converts previously lawful conduct into a criminal offense.
Eugene Ellsworth operated a coal mine under pre-1987 permits. A later statute imposes new reclamation obligations on past mining activity. Because the measure is regulatory and does not increase criminal punishment, the court upholds its application to Eugene's earlier operations.
Elijah Edwards imported enslaved persons into a state in 1805 when federal law permitted the practice. A later federal statute criminalizes the same importation. The court must refuse to apply the statute to Elijah because it retroactively punishes conduct lawful at the time it occurred.
Esme Ellington published a novel in 1995 under a copyright term that would expire in 2025. A later statute extends all existing copyrights by twenty years. Because the extension is civil and does not impose criminal punishment, the court permits its application to Esme's earlier work.
The clause bars statutes that retroactively make conduct criminal, increase punishment for completed offenses, or alter evidentiary rules to the defendant's disadvantage. It applies only to criminal or punitive measures.
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No. A measure that is civil and nonpunitive in purpose and effect may apply retroactively even if it imposes new burdens on past conduct.
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Due process prohibits courts from applying an unexpected and indefensible change in criminal law retroactively, but foreseeable evolution of doctrine is permissible.
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A change that merely alters procedure without increasing the quantum of punishment or the likelihood of conviction is allowed. Any alteration that effectively raises the risk of criminal liability for past acts is forbidden.
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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…