The Federalist Papers were a collection of published articles written by Alexander Hamilton, James Madison, and John Jay under a single pen name, Publius. There were 85 articles in all, the first was published on October 27, 1787 and the entire set was published as a book in 1788.
The purpose of the Federalist Papers was to rally support for ratification of the Constitution in New York. The Federalist Papers were one side of the debate, and were answered by the Anti-Federalist Papers. Ultimately, the Federalists won and the Constitution was adopted.
Thomas Jefferson called the Federalist Papers "the best commentary on the principles of government ... ever written." John Stuart Mill opinion was that they were "the most instructive treatise we possess on federal government." Alexis de Tocqueville was also an admirer, stating it "an excellent book, which ought to be familiar to the statesmen of all countries."