Ex Parte Quirin et al., 1942, is a landmark U.S. Supreme Court case that involved eight German saboteurs who entered the United States during World War II with plans to commit acts of sabotage. They were captured by the FBI and tried before a military tribunal, which sentenced them to death. The defendants appealed their sentences on grounds that President Roosevelt's order establishing the tribunal was unconstitutional and they should have been tried in civilian courts instead. However, the Supreme Court unanimously upheld their convictions and sentences in a per curiam decision (a ruling issued collectively by all judges), stating that as unlawful combatants engaged in hostile activities against the U.S., they could be subjected to military jurisdiction even though they had not actually committed any act of sabotage at time of capture.

In the Ex Parte Quirin case of 1942, there were no dissenting opinions. The Supreme Court unanimously upheld the jurisdiction of a U.S. military tribunal over the trial of several German saboteurs in the United States during World War II. The court ruled that President Franklin Roosevelt had authority to order a special military tribunal and that rights normally afforded under habeas corpus could be overlooked when dealing with enemy combatants during times of war.