The Federalist Papers were a series of 85 essays written by Alexander Hamilton, John Jay, and James Madison between October 1787 and May 1788. The essays were published anonymously, under the pen name "Publius," primarily in two New York state newspapers of the time: The New York Packet and The Independent Journal.
They were written to urge citizens of New York to support ratification of the proposed United States Constitution. Significantly, the essays explain particular provisions of the Constitution in detail. It is for this reason, and because Hamilton and Madison were members of the Constitutional Convention, that the Federalist Papers are often used today to help understand the intentions of those drafting the Constitution.
See also Encyclopedia: The Federalist