The state does not get unlimited chances to convict. Double jeopardy is the constitutional and common-law protection that bars the government from prosecuting or punishing a person twice for the same offense after an acquittal or conviction.

The protection attaches once a jury is sworn or, in bench trials, when the first witness is sworn. It prevents retrial after acquittal and multiple punishments for the same crime. Separate sovereigns, such as state and federal governments, may in some systems prosecute the same conduct under their own laws.

Mistrials declared for manifest necessity usually allow retrial. Appeals by the defendant that result in reversal may also permit a new trial. The doctrine forces careful charging decisions and protects individuals from repeated prosecutorial attempts to secure a conviction.

• Bar on retrial or double punishment for the same offense
• Attaches after jury or witness is sworn
• Subject to exceptions such as separate sovereigns
• Protects finality of acquittals