Definition
Stare decisis is a Latin phrase meaning to stand by things decided. It is the doctrine that once a court has settled a legal question, future courts deciding similar cases should reach the same conclusion rather than re-litigate the issue from scratch.
In the United States, the doctrine is strongest vertically: lower courts are bound by the rulings of higher courts in the same jurisdiction. It operates more loosely horizontally, where a court may revisit its own past decisions but is expected to do so only with strong justification.
Why it matters
How it works
When a court faces a dispute, it identifies the controlling legal question and searches for earlier decisions that resolved the same question. A binding precedent must be followed; a persuasive precedent from another jurisdiction may merely inform the reasoning.
Courts can also distinguish a case, arguing that the facts differ enough that the old rule does not apply. Overruling precedent is reserved for situations where the prior decision proved unworkable, was poorly reasoned, or has been undermined by later law. Because of stare decisis, even a sharply divided court usually treats settled rulings as a starting point.