Ex parte Merryman, 17 F. Cas. 144 (C.C.D. Md. 1861) (No. 9487), was a controversial U.S. federal court case during the American Civil War. It was a test of the authority of the President to suspend "the privilege of the writ of habeas corpus" under the Constitution's Suspension Clause, when Congress was in recess and therefore unavailable to do so itself. More generally, the case raised questions about the ability of the executive branch to decline to enforce judicial decisions when the executive believes them to be erroneous and harmful to its own legal powers.
John Merryman was a prominent planter from Baltimore County, Maryland, who had been arrested at his rural plantation for destroying railroad bridges on which Union troops were traveling.