A carnival atmosphere has engulfed downtown Washington, where more than a million people watched Barack Obama become the 44th President of the United States and America's first African American leader. Mr. Obama took the oath of office on the steps of the U.S. Capitol and later participated in an inaugural parade along Washington's Pennsylvania Avenue.
Joyous cheers and wild screams greeted President Obama and First Lady Michele Obama as they stepped out of the presidential limousine to walk a few blocks at the head of a parade between the Capitol and the White House.
For hundreds of thousands of people who could not gain access to the packed National Mall to view the swearing in ceremony, it was their last chance to see the Obamas before they entered the White House as America's new First Family.
Hours earlier, President Obama took the oath of office and received a military 21-gun salute.
In his inaugural address, he noted that he takes office in a time of crisis.
"Our nation is at war, against a far reaching network of violence and hatred," said President Obama. "Our economy is badly weakened - a consequence of greed and irresponsibility on the part of some - but also our collective failure to make hard choices and prepare the nation for a new age."
The president urged bold action to create new jobs and end a year-long recession, and he called on all Americans to do their part to solve the challenges confronting the nation.
"What is required of us now is a new era of responsibility, a recognition on the part of every American, that we have duties to ourselves, our nation and the world - duties that we do not grudgingly accept, but rather seize gladly, firm in the knowledge that there is nothing so satisfying to the spirit, so defining of our character, than giving our all to a difficult task," said Mr. Obama.
Mr. Obama promised to defeat those who employ violence and terrorism, and to remain true to America's core ideals while defending the nation.
The 47-year-old president is the son of a black Kenyan father and a white American mother. He grew up in Hawaii and Indonesia. And on Tuesday, he held out a friendly hand to those overseas who watched his address.
"And so to all other peoples and governments who are watching today - from the grandest capitals to the small village where my father was born - know that America is a friend of each nation and every man, woman and child who seeks a future of peace and dignity and we are ready to lead once more," continued Barack Obama.
Many African American families attended the inauguration of the country's first black president, including this woman from Pennsylvania:
"I could not be happier or more proud," she said. "I am an 81-year-old black lady who has seen an awful lot in my lifetime. And never, in all my years, did I think that this day would come and one of us would be in the White House."
Public opinion polls show that Barack Obama enjoys some of the highest approval ratings of any new president.
Presidential historian Allan Lichtman of American University says President Obama will bring major changes, in both style and substance, to the White House.
"Barack Obama represents and celebrates not only the diversity of America, but the diversity of a knit-together global world," said Allan Lichtman. "In addition, I think, so far Barack Obama has indicated that he is likely to take American foreign policy in new directions as part of this new political era."
Between the swearing in ceremony and the parade, President Obama ate lunch with U.S. senators and representatives at the Capitol. During the event, Massachusetts Senator Edward Kennedy suffered an apparent seizure and was rushed to a hospital. Kennedy was diagnosed with brain cancer last year. Another elder senator, Robert Byrd of West Virginia, also became ill and required medical attention.
Mr. Obama's inauguration closed eight years of Republican leadership under George Bush, who flew home to Texas aboard the plane Mr. Obama will use as Air Force One.