Huge crowds are expected to pack Washington's National Mall as Mr Obama takes the oath of office at exactly 1200 (1700 GMT). Unprecedented security is in place, with 40,000 security personnel either on duty or stand-by in the city.Across the US, there is a sense of history being made, correspondents say.
The roar of approval that will greet Barack Obama when he takes the oath of office will be genuine, heartfelt and will come from all corners of America, BBC North America editor Justin Webb says.
But the new president faces serious challenges. America is gripped by uncertainty as the economy faces its worst crisis in decades. Mr Obama must also handle wars in Iraq and Afghanistan, and the Israeli-Palestinian conflict. (Source: BBC News)
