United States purchasers of vitamin C sued Chinese manufacturers, alleging that the companies conspired to fix the price and quantity of vitamin C exported to the United States. The manufacturers argued that Chinese law required the challenged conduct, and China’s Ministry of Commerce submitted statements describing its domestic law. The district court declined to treat those statements as conclusive, while the Second Circuit held that a federal court was bound to accept a reasonable foreign government interpretation of its own law. The Supreme Court vacated and remanded. The federal rule governing foreign-law proof treats foreign-law questions as legal rulings and permits courts to consider any relevant source. International comity supports respectful consideration of a foreign government’s views, but neither the rule nor any statute makes those views conclusive. Their weight depends on factors including clarity, support, context, official authority, transparency, and consistency with past positions. Because the Second Circuit focused on the Ministry’s submission and did not address contrary evidence, the Supreme Court directed renewed consideration without deciding what Chinese law required.