A painting by Camille Pissarro hangs in a Spanish museum that the Nazis stole from a Jewish family in 1939. For fifteen years the parties have litigated who the rightful owner is: the museum or the family. The case may well turn entirely on whether California or Spanish law governs. It’s not uncommon for the outcome of a case to be affected by the question of which jurisdiction’s law controls. But the Supreme Court faces a question one step removed: Which rules do you apply to decide whose law controls? State choice-of-law rules or federal choice-of-law rules?

No, this is not a devious hypothetical invented by your civil procedure professor for your final exam. The Supreme Court heard argument on the question earlier this week in Cassirer v. Thyssen-Bornemisza Collection Foundation. And the painting’s fate hangs in the balance. The Court’s decision could affect choice-of-law procedures in a wide array of cases, particularly when a state-law claim is brought in federal court under a federal-question jurisdictional vehicle.