The Ex Post Facto Clause prohibits federal and state governments from retroactively creating criminal liability or increasing punishment for conduct after it occurred. A retroactive law changes the legal consequences of earlier conduct or events, but not every retroactive law is an unconstitutional ex post facto law.
The Ex Post Facto Clause is a constitutional protection against certain laws that change criminal consequences after the fact.
The U.S. Constitution contains two Ex Post Facto Clauses. Article I, Section 9 prohibits the federal government from passing ex post facto laws, while Article I, Section 10 imposes the same prohibition on the states. The Supreme Court has generally interpreted the two provisions under the same principles.
The protection reflects a basic principle of criminal law. People generally should be able to determine the criminal consequences of their conduct based on the law that existed when the conduct occurred.
A retroactive law is a law that changes the legal consequences of conduct, transactions, or events that occurred before the law took effect.
Retroactivity by itself does not make a statute unconstitutional.
Congress and state legislatures sometimes enact laws that apply to earlier conduct or existing legal relationships. The Constitution places particular restrictions on retroactive legislation, but the Ex Post Facto Clause is primarily concerned with laws that are criminal or punitive in nature.
A retroactive tax rule or civil regulatory requirement, for example, is not automatically an ex post facto law simply because it reaches past events.
The Supreme Court's traditional framework traces to Calder v. Bull, decided in 1798.
An ex post facto problem can arise when a legislature retroactively makes previously lawful conduct criminal, increases the seriousness of an offense, increases the punishment attached to a crime, or changes evidentiary rules in a way that makes conviction easier for past conduct.
The Clause therefore protects against more than the creation of entirely new crimes. A government also cannot ordinarily increase criminal punishment after the offense has already occurred.
A law described by the legislature as civil or regulatory is generally outside the Ex Post Facto Clause if it is genuinely nonpunitive.
Courts are not limited to the label placed on the statute. If a legislature describes a measure as civil but its purpose or effects make it punitive, an ex post facto challenge can still arise.
The Supreme Court applied this framework to a Sex Offender Registry and Sex Offender Registration LawsA sex offender registry is a government system that requires people convicted of specified sex offenses to provide identifying and other information to authorities, with some information often made publicly available. Federal and state law governs registration requirements, which can differ significantly by jurisdiction.Read more → law in Smith v. Doe. The Court first examined whether Alaska intended its registry as a civil regulatory system and then considered whether the law's effects were so punitive that they transformed it into criminal punishment. The Court concluded that the particular Alaska law before it was nonpunitive and could be applied retroactively without violating the Ex Post Facto Clause.
That decision does not establish that every registration law is automatically nonpunitive. Courts examining different laws can consider the structure and effects of the particular statutory scheme.
The constitutional Ex Post Facto Clauses directly restrict legislation, not judicial decisions.
The Supreme Court has nevertheless recognized that unexpected and indefensible judicial expansions of criminal liability can raise separate due process concerns. The constitutional doctrines are related but legally distinct.
The Ex Post Facto Clause limits the government's ability to change the rules of criminal punishment after conduct has already occurred.
The distinction between a retroactive law and an ex post facto law is important. Many laws can affect past events. The constitutional prohibition becomes central when legislation retroactively creates criminal liability or increases punishment.
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