Answer :

Well, the Federalist Papers were a series of 85 essays urging the citizens of New York to ratify the new U.S Constitution. Which was written by Alexander Hamilton, James Madison, and also John Jay.
 The essays were originally appeared anonymously in New York newspapers in 1787 and 1788 under the pen name "Publius."
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Hope this helped! Anymore questions, please feel free to ask! :)

The Federalist Papers were essays written by James Madison, Alexander Hamilton, and John Jay, for the purpose of urging ratification of the US Constitution. The essays originally appeared in serial fashion in several newspapers. They used the pseudonym "Publius" in sending them for publication. These 77 essays, plus 8 more, were then published in a 2-volume set in 1788, under the title, The Federalist: A Collection of Essays, Written in Favour of the New Constitution, as Agreed upon by the Federal Convention, September 17, 1787.  

Of the 85 total essays, Alexander Hamilton wrote 51. James Madison wrote 29. John Jay wrote 5.  In terms of some of the things they worte about, Jay wrote about the United States' relationships with other countries, Madison wrote about government structure, and Hamilton wrote about the weakness of the Articles of Confederation.