Tonight the world joins together and stands up to cancer. The celebrity-packed live webcast of the pre-show will begin at 7:30 PM EST/ 4:30 PM PST, and then the official Stand Up To Cancer webcast begins at 8:00 PM EST/ 5:00 PM PST and will be followed by a half hour post show. Following the live broadcast, the entire event will be available on demand online.

Musicians Billie Joe Armstrong of [lastfm]Green Day[/lastfm], [lastfm]Neil Diamond[/lastfm], [lastfm]Herbie Hancock[/lastfm], [lastfm]Kris Kristofferson[/lastfm], [lastfm]Lady Antebellum[/lastfm], [lastfm]Martina McBride[/lastfm], Ann and Nancy Wilson of [lastfm]Heart[/lastfm], [lastfm]Queen Latifah[/lastfm], and [lastfm]Stevie Wonder[/lastfm] will perform live and will be joined by celebrities like George Clooney, Lance Armstrong, Christina Applegate, Will Smith, Denzel Washington, Gwyneth Paltrow, Sally Field, Cindy Crawford, Seth Rogen, Seth MacFarlane, Tony Hawk, and many more to raise funds for innovative research to bring new therapies to cancer patients.

The broadcast will air in 195 countries, but you can watch it right here online.

Flip through the gallery below to see some of your favorite stars who are standing up to cancer.

Stand Up To Cancer gallery (pictured: Reese Witherspoon)