The "Federalist No. 78" is an essay written by Alexander Hamilton, explaining his views on the proper structure and role of the judiciary branch in a constitutional democracy. The essay was massively influential, and many of the ideas Hamilton set forth in the essay became part of the Constitution of the United States.
In "Federalist No. 78," Hamilton explains that the judiciary branch should act as a check on the constitutional power of the legislative branch by determining if laws enacted by Congress align with the powers granted them by the U.S. Constitution. In Hamilton's system, the courts may void a law that they deem unconstitutional. Hamilton insisted that the judiciary must be completely distinct from the other two branches of government, the legislative and executive. Hamilton also discussed the length of a federal judge's term in office. He felt that judges, once appointed, should remain in office as long as they display "good behavior," though he leaves the definition of good behavior vague. Most of the ideas discussed in this paper have been incorporated into the U.S. Constitution and the constitutions of numerous states.
"Federalist No. 78" is just one of 85 essays included in "The Federalist Papers," which were a series of documents written by Hamilton, James Madison and John Jay. The papers laid the groundwork for the Constitution and made the case for ratification.