The Framers of the Constitution explain why they designated the Vice President of the United States as President of the Senate, in Article I, Section 3, Clause 4 of the Constitution.

The President of the Senate has what is called a "casting vote," defined as the decisive vote of a presiding officer, when the votes of the assembly or house are equally divided.

Hamilton wrote that "to secure at all times the possibility of a definite resolution of the body, it is necessary that the President [i.e. the Vice President of the U.S.] should have only a casting vote."

The White House web site includes a home page for the Vice President of the United States, who also serves as President of the Senate.

Thomas Jefferson was the second Senate President. Section XVII of his Manual covers debate, and says that no one is to speak superfluously or tediously, and that the Senate President's decision is without appeal. This rule has since been modified.

Details about historical Senate precedents regarding the President of the Senate are provided by Riddick's Senate Procedure, in adobe acrobat (pdf) format.

The position of the Vice President as President of the Senate was borrowed from the New York Constitution.

Detailed description of the role of the Vice President of the United States as President of the Senate.

The Constitution gives the Vice President of the United States power to vote when the Senate is equally divided, and the Senate Historian has listed all of those occasions when the Senate President has broken a tie vote.