Marbury v. Madison was the first significant decision handed down by the U.S. Supreme Court after John Marshall was sworn in as its chief justice in 1801. In Marbury, for the first time, the Supreme Court declared an act of Congress unconstitutional; it would not do so again until Dred Scott v. Sandford struck down the Missouri Compromise in 1857. Marbury was not the Court’s first exercise of judicial review—the power to determine the constitutionality of legislative and administrative acts—but by declaring the Court the final arbiter of constitutional questions, this seminal decision fully empowered the third branch of government, making the concept of federal checks and balances a reality.