The United States Capitol building features a central rotunda below the Capitol dome. Built between 1818 and 1824, the rotunda has been described as the Capitol's "symbolic and physical heart".

The rotunda is connected by corridors leading south to the House of Representatives and north to the Senate chambers. To the immediate south is the semi-circular National Statuary Hall, which was the House of Representatives chamber until 1857. To the northeast is the Old Senate Chamber, used by the Senate until 1859 and by the Supreme Court until 1935.

The rotunda is 96 feet (29 m) in diameter, rises 48 feet (15 m) to the top of its original walls and 180 feet 3 inches (54.94 m) to the canopy of the dome, and is usually visited daily by thousands of people. The space is a national showcase of art, and includes numerous historical paintings and sculptures. It is also used for ceremonial or public events authorized by concurrent resolution of both houses of congress, including the lying in state of honored dead.

William Thornton, a physician and architect, was the winner of the contest to design the Capitol in 1793. Thornton had first conceived the idea of a central rotunda. However, due to lack of funds or resources, oft-interrupted construction, and the British attack on Washington during the War of 1812, work on the rotunda did not begin until 1818. The rotunda was completed in 1824 under Architect of the Capitol Charles Bulfinch, as part of a series of new buildings and projects in preparation for the final visit of Marquis de Lafayette in 1824. The rotunda was designed in the neoclassical style and was intended to evoke the design of the Pantheon.

The sandstone rotunda walls rise 48 feet (15 m) above the floor. Everything above this, including the Capitol dome, was designed in 1854 by Thomas U. Walter, the fourth Architect of the Capitol. Walter had also designed the Capitol's north and south extensions. Work on the dome began in 1856, and in 1859, Walter redesigned the rotunda to consist of an inner and outer dome, with a canopy suspended between them that would be visible through an oculus at the top of the inner dome. In 1862, Walter asked painter Constantino Brumidi to design "a picture 65 feet (20 m) in diameter, painted in fresco, on the concave canopy over the eye of the New Dome of the U.S. Capitol". At this time, Brumidi may have added a watercolor canopy design over Walter's tentative 1859 sketch. The dome was being finished in the middle of the American Civil War and was constructed from fireproof cast iron. During the Civil War, the rotunda was used as a military hospital for Union soldiers. The dome was finally completed in 1866.

Originally the crypt had an open ceiling into the rotunda. Visitors can still see the holes in the stone circle that marked the rim of the open space in the rotunda floor. Underneath the floor of the crypt lies a tomb that was the intended burial place for George Washington. After a lengthy battle with his estate and the commonwealth of Virginia, however, plans for him to be buried in the crypt were abandoned.

In January 2013, the Architect of the Capitol announced a four-year, $10 million project to repair and conserve the Capitol Dome's exterior and the Capitol rotunda. The proposal required the stripping of lead paint from the interior of the dome, repair to the ironwork, repainting of the interior of the dome, rehabilitation of the interstitial space between the dome and rotunda, and installation of new lighting in the interstitial space and the rotunda. The dome and rotunda, which were last conserved in 1960, were showing significant signs of rust and disrepair. There was a danger that decorative ironwork could have fallen from the rotunda to the space below, and that weather-related problems could damage the artwork in the rotunda. Without immediate repair, safety netting was installed, temporarily blocking the rotunda's artwork from view.

Eight niches in the rotunda hold large, framed historical paintings. All are oil-on-canvas and measure 12 by 18 feet (3.7 by 5.5 metres). Four of these are scenes from the American Revolution, painted by John Trumbull, who was commissioned by Congress to do the work in 1817. These are Declaration of Independence, Surrender of General Burgoyne, Surrender of Lord Cornwallis, and General George Washington Resigning His Commission. These were placed between 1819 and 1824. Between 1840 and 1855, four more paintings were added. These depicted the exploration and colonization of America and were all done by different artists. These paintings are Landing of Columbus by John Vanderlyn, Discovery of the Mississippi by William Henry Powell, Baptism of Pocahontas by John Gadsby Chapman, and Embarkation of the Pilgrims by Robert Walter Weir.^{[citation needed]}