will.i.am, John Legend, Katy Perry and Usher were among the stars who helped kick off U.S. President Barack Obama's inauguration celebrations in Washington, D.C. on Saturday (19Jan13).

A whole host of famous faces descended on the U.S. capital as Obama prepares to be sworn in for a second term in front of hundreds of thousands of people on the National Mall on Monday (21Jan13).

Black Eyed Peas star will.i.am was at the star-studded OurTime.org Generation Now party, where Legend, Common and T-Pain performed in honour of the next generation of American voters.

will.i.am talked about the importance of youth activism, telling reporters, "This is important for the youth to realise how powerful they are and to stay active and stay informed, and go out when it's time to vote. And not just for a presidential candidate, but for local government, too."

Meanwhile, pop star Perry and Usher were headliners at the Kids Inaugural Concert at the Washington Convention Center for children of American military families.

Rapper/actor Nick Cannon served as emcee, and Glee cast members Darren Criss, Naya Rivera and Amber Riley also took the stage to entertain the kids.

Perry debuted an Uncle Sam-style corset and performed hits including Teenage Dream and Firework, which was accompanied by a video montage featuring photos of President Obama with children.

Kelly Clarkson, Beyonce, Stevie Wonder, Alicia Keys, fun. and Cyndi Lauper are all gearing up to perform at events related to Obama's inauguration, while Lady Gaga will reportedly sing at a private ball for the president's campaign staff on Tuesday (22Jan13).