"An inauguration is a reminder that here in the United States, even after occasionally savage disagreements, we transfer power peacefully," said presidential historian and ABC News consultant Richard Norton Smith.
"Inaugurating the first African-American president is of enormous significance and adds an extra dimension and extra pride to the ceremonies, not just for African-Americans but for all Americans," he said.
Obama and Biden arrived in Washington, D.C., by train following a route that mirrored Abraham Lincoln's preinaugural trip in 1861.
Obama, who has struck a tone of confidence and cooperation during the transition, enters office with higher approval ratings than any incoming president since Ronald Reagan was inaugurated in 1981. Seventy-nine percent of Americans hold a favorable opinion of him.
The newly sworn in President Obama and the new first lady Michelle Obama are expected to attend seven official inaugural balls this evening. The first couple is expected to dance their first dance at the Neighborhood Ball to the Etta James classic "At Last" sung by Beyonce Knowles.