In the United States, the office of the president of the Senate is held by the nation’s vice president. Despite what his title may suggest, in practice, the duties of the president of the Senate are generally fairly few. His main responsibilities include casting votes when ties have occurred and occasionally presiding over the Senate in a ceremonial capacity. When the Senate's president is not present — as regularly happens — an elected figure called the president pro tempore presides over the Senate.

Perhaps the most significant power awarded to the president of the Senate is that of casting deciding votes. This prerogative is exercised only when the results of a Senate vote on a given issue are equally split. In this case, the President of the Senate — if present — may opt to vote, thereby deciding the issue. If he is absent in a tie situation, the motion fails. It is only when the Senate has arrived at a tie that the president of the Senate is allowed to cast a vote.

At times, the Senate’s president also presides over ceremonial events. He may, for instance, be present to swear in new senators. In addition, he may preside on those occasions when the Senate and the House of Representatives meet together for shared discussion or to listen to an address given by the US president. These meetings are known as joint sessions.

As the individual serving as the president of the Senate is simultaneously serving as the United States vice president, he is frequently detained by executive duties and is thus unable to preside over a large proportion of Senate activities. Consequently, an elected senator frequently takes over the day-to-day duties of leading Senate business. This figure is known as the president pro tempore.

Though the president pro tempore must win his seat through a Senate election, in most cases, he is the longest-serving member of the Senate majority party. His job is to preside over the Senate when the president of the Senate cannot be present. The day-to-day tasks involved in presiding over the Senate include pronouncing vote results and inviting senators to address the chamber.

Often, however, the president pro tempore passes on these daily duties to junior senators from the majority party. These junior senators preside over the Senate for short periods. This experience enables them to gain a valuable working knowledge of Senate policies and processes.