Today is called "Super Tuesday" because there are Republican contests in 10 states and 419 delegates at stake.
The states: Alaska, Georgia, Idaho, Massachusetts, North Dakota, Ohio, Oklahoma, Tennessee, Vermont and Virginia.
The timeline: Polls start closing in the East at 7 p.m. EST, with winners probably being declared in Georgia, Virginia and Vermont soon after that.
The showdown state: It's Ohio, where Mitt Romney and Rick Santorum are running neck and neck.
Romney will spend the day in Massachusetts, where he will vote at 5:15 p.m. EST in Belmont, and he'll attend an election night party at 9:30 p.m. in Boston. He's expected to win in Massachusetts, but a lot of voters in the state are not exactly in a fever pitch over him.
Santorum will spend the day in Ohio, and head to an election night party in Steubenville that begins at 8 p.m. EST. Upsetting Romney in Ohio would be a major boost to Santorum's campaign for the GOP nomination.
Next Gingrich will spend the day in his home state of Georgia, except for a midday campaign swing in Alabama, which holds its primary March 13. His campaign's election night party starts at 6:30 p.m. EST. Gingrich has a double-digit lead in the polls and is expected to win easily.
Ron Paul, who is yet to win a state in the nomination battle, will spend the day campaigning in Idaho and North Dakota. There was no election night party listed on his agenda.
Romney, Gingrich and Santorum will speak at the American Israel Public Affairs Committee Policy Conference in Washington, D.C. Romney and Gingrich will speak via live video, and Santorum in person.
But not all the attention will be on Super Tuesday and the GOP candidates. President Obama will hold his first national news conference since November at 1:15 p.m. EST. He also will meet with Business Roundtable members to discuss jobs and economic growth.
And then there is this: Alan Greenspan, chairman of the Federal Reserve Board from 1987 to 2006, turns 86 on Tuesday.
Sources: Yahoo! News, Associated Press.
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- Rick Santorum
- Mitt Romney