Viewers will be reunited with some of the most memorable, entertaining and controversial Houseguests from previous installments of Big Brother when the 20 candidates vying to compete in the all-stars edition are unveiled during Big Brother All-Stars: America's Choice. The special primetime casting episode, which kicks off the season, will be broadcast on Wednesday, June 21 at 8:00 PM on the CBS Television Network.

For the first time in Big Brother history worldwide, viewers will have the opportunity to vote which former Houseguests should compete this season with American television viewers choosing half of the houseguests who will ultimately enter the Big Brother house.

A few hours after the casting episode is broadcast (8:00-9:00 PM ET/PT), viewers can cast their votes online at CBS.com. The polls will close on Wednesday, June 28 at 11:59 PM ET/8:59 PM PT.

Each potential "All Star" introduced on the casting episode will have their own profile on CBS.com, which will include "Why you should vote for me" text and video, as well as clips from their past appearance on Big Brother.

Additionally, throughout the voting process, candidates will be able to campaign for themselves and will be encouraged to use any reasonable means they can to state their case to America as to why they should be voted into the Big Brother 7: All-Stars house.

During the premiere of Big Brother 7: All-Stars, all 20 finalists will be present and awaiting the news of who will play the game. Host Julie Chen will announce the lucky 12, who will immediately enter the house.

Big Brother 7: All-Stars will follow the relationships and conflicts of players who live together in a house outfitted with dozens of cameras and microphones recording their every move 24 hours a day. One by one, the houseguests will vote each other out of the house. At the end of three months, the last remaining houseguest will receive the grand prize of $500,000. While living together in a confined space won't be anything new to the houseguests, choosing between any pre-existing relationships and building new alliances could be a challenge.