The Federalist Papers are a series of 85 articles advocating the ratification of the United States Constitution. Seventy-seven of the essays were published serially in The Independent Journal and The New York Packet between October 1787 and August 1788. A compilation of these and eight others, called The Federalist; or, The New Constitution, was published in two volumes in 1788 by J. and A. McLean. The series' correct title is The Federalist; the title The Federalist Papers did not emerge until the twentieth century.

The Federalist remains a primary source for interpretation of the U.S. Constitution, as the essays outline a lucid and compelling version of the philosophy and motivation of the proposed system of government. The authors of The Federalist wanted both to influence the vote in favor of ratification and to shape future interpretations of the Constitution. According to historian Richard B. Morris, they are an "incomparable exposition of the Constitution, a classic in political science unsurpassed in both breadth and depth by the product of any later American writer."

At the time of publication, the authorship of the articles was a closely-guarded secret, though astute observers guessed that Hamilton, Madison, and Jay were the likely authors. Following Hamilton's death in 1804, a list that he drew up became public; it claimed fully two-thirds of the essays for Hamilton, including some that seemed more likely the work of Madison (Nos. 49-58, 62, and 63). The scholarly detective work of Douglass Adair in 1944 postulated the following assignments of authorship, confirmed in 1964 by a computer analysis of the text:

• Alexander Hamilton (51 articles: nos. 1, 6–9, 11–13, 15–17, 21–36, 59–61, and 65–85)
• James Madison (29 articles: nos. 10, 14, 37–58 and 62–63)
• John Jay (5 articles: 2–5 and 64).
• Nos. 18–20 were the result of a collaboration between Madison and Hamilton.

The authors used the pseudonym "Publius," in honor of Roman consul Publius Valerius Publicola. Madison, whom posterity generally credits as the father of the Constitution despite his repeated rejection of the honor during his lifetime, became a leading member of the U.S. House of Representatives from Virginia (1789-1797), Secretary of State (1801-1809), and ultimately the fourth President of the United States. Hamilton, who had been a leading advocate of national constitutional reform throughout the 1780s and represented New York at the Constitutional Convention, in 1789 became the first Secretary of the Treasury, a post he held till his resignation in 1795. John Jay, who had been secretary for foreign affairs under the Articles of Confederation from 1784 through their expiration in 1789, became the first Chief Justice of the United States in 1789, stepping down in 1795 to accept election as governor of New York, a post he held for two terms, retiring in 1801.

There are many highlights among the essays comprising The Federalist. Federalist No. 10, in which Madison discusses the means of preventing rule by majority faction and advocates an extended republic, is generally regarded as the most important of the 85 articles from a philosophical perspective; it is complemented by Federalist No. 14, in which Madison takes the measure of the United States, declares it appropriate for an extended republic, and concludes with a memorable defense of the constitutional and political creativity of the Federal Convention. In Federalist No. 84, Hamilton makes the case that there is no need to amend the Constitution by adding a Bill of Rights, insisting that the various provisions in the proposed Constitution protecting liberty amount to a bill of rights. Federalist No. 78, also written by Hamilton, lays the groundwork for the doctrine of judicial review by federal courts of federal legislation or executive acts. Federalist No. 70 presents Hamilton's case for a one-man chief executive. In Federalist No. 39, Madison presents the clearest exposition of what has come to be called "Federalism." In Federalist No. 51, Madison distills arguments for checks and balances in a memorable essay often quoted for its justification of government as "the greatest of all reflections on human nature."