Welcome to our live coverage of the public inauguration of Barack Obama as president of the United States. We will be bringing you live updates and analysis from the BBC's correspondents in Washington DC and beyond, streaming live video of the ceremonies, updating with the best of the comment on blogs and social networks, or sent to us via email, and also taking in the best pictures of the day.
Not as many people are expected to attend as the 1.8 million who came to Mr Obama's inauguration for his first term, reports the BBC's Laura Trevelyan - who is already on the scene in Washington as dawn breaks - but hundreds of thousands nonetheless.
The inauguration has already been touched by controversy after rapper Lupe Fiasco criticised President Obama's stance on Israel's recent bombardment of Gaza as he performed at an inauguration party on Sunday night. He was eventually escorted from the stage. You can read more at Politico.
Mr Obama won a second term in office in November more comfortably than many expected, taking 332 electoral college votes to defeat Republican Mitt Romney - well past the 270 he needed. But the popular vote was close and the Republicans retained control of the House of Representatives. Mr Obama leads a divided nation and is likely to face a tough task if he tackles contentious issues over the next four years.
As dawn breaks, crowds are already gathering in front of the Washington Monument, with over three hours to go until the inauguration.