Welcome to our live coverage of the Super Tuesday Republican primary and caucus votes. With 10 states voting today, a clear across-the-board win for any one candidate could well bring some clarity to what has so far been a long race full of twists and turns. Will that be outcome? Follow us here for all the latest news, analysis, tweets, pictures and results throughout the day.
Super Tuesday can make or break a candidacy, but today's contest is unlikely to crown a clear Republican nominee. Mitt Romney is still the front-runner but Rick Santorum, Newt Gingrich and Ron Paul are all expected to pick up some delegates as they seek to stay in the race.
1217 Ian Pannell,, BBC News, Columbus, Ohio
Blue skies over Columbus, Ohio on the biggest day in the nomination calendar. Polls have Santorum and Romney too close to call in this key state. Steady voting underway.
Primary season for the Republicans has had no shortage of ups and downs. There have been about 20 debates, most televised, with several candidates peaking in popularity before official voting began in January.
Since the first votes were cast in Iowa and New Hampshire in early January, former Pennslyvania Senator Rick Santorum has seen a surge in his popularity. After a hat-trick of wins in early February, Mitt Romney's campaign and its allies have come down hard against him, launching waves of ads and seeking to label him as a career politician tainted by years in Washington.
Katty Kay, Washington Correspondent, BBC World News America
tweets: Romney cld well close deal today but IF economy continues to pick up his rationale for running weakens - he'll need to broaden appeal.
Mr Romney, who has won the lion's share of his delegates in Florida, New Hampshire and Arizona, has spent millions on his campaign but has not won the hearts of conservative voters. Newt Gingrich, House speaker during the Clinton administration, has tussled with Mr Santorum for voters who describe themselves as "very conservative".
Texas Congressman Ron Paul has taken a more unconventional approach to campaigning since the early January contests. He has focused his efforts on the Western caucus states, where his support is stronger and the process can benefit him. He even campaigned in Alaska, a rare stop for a presidential candidate.
To win the Republican nomination, a candidate needs 1,144 delegates. Check where the candidates stand right now with our handy delegate tracker. A total of 424 delegates are up for grabs today.