The President pro tempore is the second-highest-ranking official of the United States Senate, after the Vice President. The Constitution instructs the Senate to choose a President pro tempore to preside over the Senate in the absence of the Vice President. Although the Constitution does not specify who can serve as President pro tempore, the Senate has always elected one of its members to serve in this position. Since the mid-20th century, tradition has dictated that the senior member of the majority party serve as President pro tempore.

In addition to presiding over the Senate, the President pro tempore fulfills a number of other responsibilities. For example, in consultation with Senate leaders, the President pro tempore appoints the director of the Congressional Budget Office (jointly with the Speaker of the House), as well as Senate legislative and legal counsel. The President pro tempore also makes appointments to various national commissions and advisory boards and receives reports from certain government agencies.

The President pro tempore may administer all oaths required by the Constitution, may sign legislation, and may jointly preside. The President pro tempore is authorized to perform certain duties in the absence of the Vice President, including ruling on points of order. Additional duties include appointment of various congressional officers, certain commissions, advisory boards, and committees. The President pro tempore is the designated legal recipient of various reports to the Senate, including War Powers Act reports under which they, jointly with the Speaker, may require the President to call Congress back into session. The officeholder is an ex officio member of various boards and commissions.