The U.S. Court of Appeals for the Second Circuit heard arguments over whether long-running claims against the Kingdom of Saudi Arabia arising from the September 11 attacks can continue, putting renewed focus on one of the most consequential sovereign-immunity disputes in modern U.S. litigation. The appeal asks whether claims brought by families of 9/11 victims may proceed despite Saudi Arabia’s effort to end the case.

At the center of the dispute is the intersection of foreign sovereign immunity, terrorism-related civil liability, and the procedural demands of mass-injury litigation that has stretched across decades.