The Supreme Court's decision in Marbury v. Madison has had long-term significance because it has established the Court's authority as the final word on the constitutionality of legislation and executive acts. The Marshall Court decided against William Marbury in the case, ruling that one part of the Judiciary Act of 1789 was unconstitutional, and thus, null and void, according to Marshall's written opinion:
Certainly all those who have framed written constitutions contemplate them as forming the fundamental and paramount law of the nation, and consequently, the theory of every such government must be, that an act of the legislature, repugnant to the constitution, is void.
In case the significance of this statement eluded the reader, Marshall went on to assert the power of the federal judiciary even more forcefully:
It is emphatically the province and duty of the judicial department to say what the law is. Those who apply the rule to particular cases, must of necessity expound and interpret the rule. If two laws conflict with each other, the courts must decide on the operation of each.
It followed that for judicial review to be meaningful, it had to be lasting, a fact that would have been obvious to readers familiar with the common law emphasis on precedent. Thus the Supreme Court claimed the power of judicial review, an enormous power, as subsequent court cases have shown. The Supreme Court has served as a check on Congress and the Executive ever since this decision, much to the frustration of both.