The Democratic Caucus of the United States Senate, sometimes referred to as the Democratic Conference, is the formal organization of all senators who are part of the Democratic Party in the United States Senate. For the makeup of the 118th Congress, the caucus additionally includes three independent senators who caucus with the Democrats, bringing the current total to 51 members. The central organizational front for Democrats in the Senate, its primary function is communicating the party's message to all of its members under a single banner. The present chair of the Senate Democratic Caucus is Chuck Schumer of New York.

Oscar Wilder Underwood was an American lawyer and politician from Alabama, and also a candidate for President of the United States in 1912 and 1924. He was the first formally designated floor leader in the United States Senate, and the only individual to serve as the Democratic leader in both the Senate and the United States House of Representatives.