Marbury v. Madison was a landmark U.S. Supreme Court case in which the Supreme Court formed the basis for the exercise of judicial review under the Constitution. The 1803 case defined the boundary between the executive and judicial branches of government.
Marbury v. Madison arose in the early days of the Republic when the Federalist and Republican parties struggled over how to define the role of the federal government. At issue in the case was whether a Judiciary Act passed by Congress, and pursuant to which a commission for a judicial appointment for William Marbury was to be delivered, was constitutional. The court determined that the Judiciary Act (of 1789) was itself unconstitutional and that the court alone could make that determination.
The Constitution did not specifically delegate the power of judicial review to any one branch, and the executive and legislative branches might have argued in 1803 that they were equally entitled as the judicial branch to be entrusted with the power of judicial review. The Supreme Court ruled unanimously. Chief Justice John Marshall wrote these famous words that are now engraved on the wall of the Supreme Court building: "It is emphatically the province and duty of the judicial department to say what the law is."