Barack Obama will be inaugurated as the nation's 44th president on January 20, continuing the tradition of a peaceful transfer of power from one leader to another that began with George Washington's first inauguration in 1789.
Modern-day presidential inaugurations are elaborate affairs, with a large crowd gathered in front of the U.S. Capitol building in Washington, followed by a parade and inaugural balls.
The inaugural tradition has pretty humble roots. The nation's first president, George Washington, took the oath of office on a balcony in New York City in 1789. New York was the nation's first capital.
The inauguration of a new president is required by the U.S. Constitution, and the oath is traditionally administered by the Chief Justice of the United States. The oath itself binds the new president to faithfully execute his office and preserve, protect and defend the Constitution.
Legend has it that George Washington added the words, so help me God at the end of the oath, but some historians now dispute that. Still, most presidents have spoken those words at their inauguration.
Presidential inaugurations also have become powerful symbols of American democracy.
Marvin Kranz is an expert on inaugurations, now retired from the Library of Congress.
"I would say that this is one of the great events in what we might call civil religion in this country. Even though most of the presidents have talked about being inaugurated under the auspices of Almighty God, nevertheless it is basically a very civil ceremony and it is something that takes place every four years, war or peace, no matter what," he said.
Another important part of the ceremony is the inaugural address in which the new president talks about where he would like to take the country during the next four years.
Relatively few inaugural addresses have stood out over the years, and those that did generally were delivered at times of national crisis.
Stephen Hess is a political scholar at the Brookings Institution in Washington.
"Abraham Lincoln, both on the eve of the Civil War trying to hold the nation together, and then Lincoln again toward the end of the Civil War about what peace could be. Franklin Roosevelt in the Great Depression of 1933. The only really great address which was not, in a sense, about a moment like this, but really about grand rhetoric, was John Kennedy's address in 1961," he said.
Franklin Roosevelt's first inaugural in 1933 is remembered because of the new president's efforts to reassure the public that all would be well despite the economic depression. His most famous line from that speech was, "We have nothing to fear but fear itself."
"This great nation will endure as it has endured. We will revive and we will prosper." said Roosevelt.
Presidential inaugurations are often symbolic of political and sometimes generational change in the United States.
President John Kennedy ushered in a new political era with his Inaugural Address in 1961.
"Let the word go forth from this time and place to friend and foe alike that the torch has been passed to a new generation of Americans, born in this century, tempered by war, disciplined by a hard and bitter peace," he said.
Twenty years later, in the midst of an economic downturn, President Ronald Reagan signaled another political shift in Washington.
Mr. Reagan's most famous line was that, "Government is not the solution to our problem. Government is the problem."
"It is time to check and reverse the growth of government, which shows signs of having grown beyond the consent of the governed," he said.
William Henry Harrison holds the record for the longest Inaugural Address. He spoke for more than an hour and half in the cold and snow of the inauguration of 1841. He developed pneumonia and died a month later, and is remembered for having the shortest tenure of any U.S. president.
Even if a president's inaugural address is long forgotten, the inauguration ceremony remains important as a kind of celebration of American democracy and the peaceful transfer of power.
Expert Marvin Kranz said the sight of the outgoing and incoming president on the same platform helps to unify the country after a divisive political campaign.
"We have done this time and time again. Every four years since 1789 and there has never been a revolution, there has never been a chance of an armed fight. It simply has taken place. We have accepted this. Not everybody liked it. For example, when Thomas Jefferson was inaugurated in 1801, John Adams, the previous president who was defeated for re-election, kind of snuck out of Washington and was not present. These days, even though they may not care for each other, the former president, if there has been a change, rides with the president from the White House to the inaugural stand," said Kranz.
As the first African-American president, Barack Obama sees a special connection with the nation's 16th president, Abraham Lincoln, a hero to many black Americans for his leadership during the Civil War.
Mr. Obama will honor Lincoln by taking the oath of office with his hand placed on the same Bible that Lincoln used during his first inauguration in 1861.