Trump gave a thumbs-up just before coming out.
Did you know?
Since 1937, U.S. vice presidents are also sworn into office at the same ceremony as presidents. Before that, it was in the Senate chamber. The vice president-elect takes the oath first, too, followed by the president-elect around noon.
Several journalists have shared these images on Twitter comparing the crowds at Obama's inauguration in 2009 and the crowds today.
The earlier rain has cleared up. Inauguration Day used to take place in March, but was moved forward to shorten the "lame-duck" period when an outgoing president remains in office. The 20th Amendment of the U.S. Constitution moved it up to end presidential terms on January 20.
The ceremony has begun to inaugurate the 45th U.S. president.
Senator Roy Blunt of Missouri, who chairs the congressional inaugural committee, was the first speaker. Now prayers, six of them by various religious leaders, will follow.
From a few minutes ago:
Our correspondent Mike Eckel live on Facebook: Police face off with protesters few blocks north of National mall.
Reports say New Destiny Christian Center's pastor Paula White, delivering a prayer now, is the first clergywoman to deliver a prayer at a presidential inauguration.
Musical portion of the program.
The vice president's swearing-in will take place first, then after that, the president's.
Senator Chuck Schumer of New York, a Democrat, is addressing the ceremony.
He mentions threats America faces, "foreign and domestic," but says he's confidence in the country for "one reason: You, the American people."