Under res judicata, when may a federal court preclude a case that involves the same claim previously litigated in state court?

• A. There is a final judgment on the merits in the prior action, and the parties and the claims are the same (or could have been raised).
• B. Whenever a state court dismissed the prior action.
• C. Only when the prior action involved the same judge.
• D. Only in criminal cases.

Answer: (A)

Res judicata (claim preclusion) bars a later federal case when the prior state court action ended with a final judgment on the merits, and the same parties (or their privies) and the same claim (or a claim that could have been raised in that action) are involved. In other words, once there’s a genuine, on-the-merits adjudication between the same parties about the same cause of action, you can’t relitigate it in federal court. Federal courts give that state court judgment the same effect as the state would, under full faith and credit, so the prior judgment precludes later litigation.

Dismissals that aren’t on the merits don’t trigger preclusion, so a state court’s dismissal isn’t necessarily a bar. The requirement isn’t about having the same judge, and res judicata isn’t limited to criminal cases; it applies to civil actions as well.