Ex post facto law

What ex post facto law means

In short, ex post facto law is a term you will meet in court papers, rules and legal research. The definition above gives its usual meaning in American civil practice. However, the exact meaning can depend on the rule, statute or court decision that uses it. So it helps to read the term in context.

Where ex post facto law comes up

The term is used across many kinds of cases. For example, you may see it in pleadings, motions and court orders. To see it in context, browse the motions and procedures library or the Learn the Law topics.

How to research the term

First, read the term where it actually appears. A rule, statute or court decision may define it for its own purposes. Next, check whether your court has a local rule that uses ex post facto law in a special way. Then look at recent decisions from courts in your jurisdiction. They show how judges apply the term today. Also, remember that state law can differ from federal law. For that reason, use our state procedures guide to find your state’s rules. Finally, confirm every source is current before you rely on it.

You can read the current federal court rules online for free.

Related legal terms

• Estoppel: a rule that stops a person from asserting a fact or right that contradicts his or her own earlier words or conduct, when another person reasonably relied on them.
• Evidence: testimony, documents and things offered to prove or disprove facts.
• Ex parte: latin for "from one side." An action, application or communication by or for one party without the other party present or notified.
• Ex parte communication: a communication about a case between the judge and one side, made outside the presence of the other parties or their lawyers.

Why precise terms matter

Courts read legal terms closely. As a result, knowing the exact meaning of a word helps you follow orders, rules and filings. Each glossary entry on Lawtopolis is short on purpose and links to the pages where the term is used.