If no candidate receives at least 50% of the vote in the primary, a runoff will be held between the top two vote-getters.

Voters who voted in a party's primary, can vote only in the runoff of the same party. Voters who did not vote in the primary, may vote in either party's runoff.

The primary is for Democratic and Republican candidates only. Candidates running unopposed for their Party's nomination will not appear on primary ballots.

The Constitution, Independence, Green, Labor, Libertarian, United Citizens, and Working Families Parties nominate by convention rather than by primary.

Voters may not vote in a political party’s runoff if they voted in another political party’s primary. However, voters who did not vote in either politicial party’s primary may vote in either politicial party’s runoff.

A defeated primary candidate may not actively offer or campaign as a write-in candidate for the ensuing election. The use of posters or stickers on the ballot is not permitted. The voting machine provides for a voter to write-in a candidate. Write-in votes are not allowed in primary elections or the election of President or Vice-president.

While the state permits fusion (a candidate may be nominated by multiple parties), if a candidate runs for and looses a primary (of any party), the candidate cannot appear on the November ballot.

South Carolina gained 1 U.S. House seat in the 2010 Census and will elected 7 Representatives in 2012.