Non bis in idem (sometimes rendered non-bis in idem or ne bis in idem) which translates literally from Latin as 'not twice in the same [thing]', is a legal doctrine to the effect that no legal action can be instituted twice for the same cause of action. It is a legal concept originating in Roman civil law, but it is essentially the equivalent of the double jeopardy doctrine found in common law jurisdictions, and similar peremptory plea (autrefois acquit/convict, 'previously acquitted/convicted') in some modern civil law countries.

The International Covenant on Civil and Political Rights guarantees the right to be free from double jeopardy; however, it does not apply to prosecutions by two different sovereigns (unless the relevant extradition treaty or other agreement between the countries expresses a prohibition). The Rome Statute of the International Criminal Court employs a modified form of non bis in idem.