The heirs of Lilly Cassirer sued a Spanish foundation over ownership of Camille Pissarro’s painting Rue Saint-Honoré in the Afternoon, Effect of Rain, which had been taken from Cassirer’s family during the Nazi era and later entered the foundation’s collection. The dispute arose under the Foreign Sovereign Immunities Act, which makes a foreign state or instrumentality liable in the same manner as a private party when an exception to immunity applies. The Supreme Court held that a federal court deciding the substantive property claim must use the forum State’s ordinary choice-of-law rules, not a federal common-law rule. The Court reasoned that the Act does not displace the normal state-law choice-of-law analysis for non-federal claims. It vacated the Ninth Circuit’s judgment and remanded for further proceedings applying California’s choice-of-law rules.