This state of 3 million people could make or break the lifelong hopes of contenders and the prayers of their supporters, and in the end, it could propel a candidate to the White House while dooming others to has-been status.
Tonight, a small percentage of Iowans will meet at their local high schools, firehouses and city halls to officially choose a presidential candidate in the first step toward narrowing the field of Republican and Democratic contenders.
Polls show a neck-and-neck race in Iowa on the Republican side between two former governors, Mike Huckabee and Mitt Romney, and an even tighter race between Democratic Sens. Hillary Clinton and Barack Obama and former Sen. John Edwards.
After raising and spending millions of dollars, and countless speeches and commercials, the wide-open race for the presidency starts its final stride tonight.
"The point is, this is the first real vote, as opposed to opinion polls," says Alan LichtÂman, a political historian at American University in Washington.
While it may not be perfect, the results of the Iowa caucuses are seen as the first gauge of electability, he says, though candidates have lost the contest and still won the presidency. In fact, just two - George W. Bush and Jimmy Carter - won Iowa and went on to occupy the Oval Office.
Candidates, though, have staked a lot on winning the caucuses - really more of a beauty contest because the victor doesn't leave with any actual delegates. And a win here could mean momentum, an increased money flow and possibly the cover of Time and Newsweek.
Some contenders need a strong showing in Iowa to avoid going bust, such as Huckabee on the GOP side and Edwards on the Democratic side, while others have built up enough campaign structure in other states to finish back and still be formidable going forward.
"If John Edwards is going to stay in, he's going to have to do well in Iowa," says University of Iowa political scientist Bruce Grondeck.
"He's been able to use personal appeal [to compete in Iowa, but] he's going to have to do more than that to win in the other states."
As for Huckabee, Grondeck says the ordained Southern Baptist minister is doing well in Iowa and South Carolina, two states with large evangelical voter blocs. But, Grondeck says, "If he doesn't win Iowa, that will blunt South Carolina. Romney doesn't have to do as well because he's got a lot of money."
But with Iowa being the first test of the presidential race, the students taking this exam are tired of cramming and are excited to whip out their No. 2 pencils and begin.
On the ground: It's just before 9 a.m. on Tuesday, and Mary Hermann's home is jammed with video cameras, reporters wielding notebooks, neighbors donning stickers and stoic security officers.
The Hermann family football-watching party has turned into a national news spectacle because of an important guest dropping by.
Romney's campaign has arranged for a quick visit by the candidate in hopes of making him seem more human and less plastic, as critics have charged.
"Not in my wildest dreams would I have guessed on New Year's Day I would have Mitt Romney in my home, but I'm just honored," she says, standing among a dozen people crowded into her kitchen. "It's a privilege to have my friends and family here to hear him speak."
That's part of the personal touch of the Iowa caucuses. While the rest of the nation may be seeing candidates on their TV screens, Iowans see them in their coffee shops, diners, pubs and churches.
The old joke goes that when asked for whom they will vote, Iowans often say, "I don't know. I've only met the candidates a couple times."
It hasn't always been that way.
Before 1972, the Iowa caucuses went unnoticed on the national stage. Few candidates spent any time on the stump in the mostly rural state. But then the raucous 1968 Democratic Convention - where delegates chosen mainly by party bosses caused a backlash - prompted some to reconsider the process by which nominees were picked.
In 1972, candidates started to pay attention to Iowa because it happened to have the first contest of the year.
Republican candidates later followed suit, and the path to the American presidency soon started in the cornfields of the Hawkeye State.
Presidential contenders now set up shop in Des Moines or nearby, hire field operatives, saturate the airwaves and make it a goal to meet as many of the voters here as possible.
Iowan Chad Ziesman has met five presidential candidates and is now deciding between Huckabee, Romney and former Tennessee Sen. Fred Thompson before he goes to his caucus meeting in Urbandale.
He says Iowa is important in the process because voters here take the job of selecting candidates very seriously.
In fact, it is amazing to see hundreds of people gathered at a local coffee shop early Sunday morning to hear candidates rattle off a list of their goals.
"We take the time to attend these things, we want to make the right decisions," says Ziesman, who manages retirement accounts. Candidates "give the time due, and [voters] give the time back and do research and figure out what they want to do with their vote."
Game time: Republicans will hit their caucus meetings at 5:30 Mountain Standard Time tonight, and it shouldn't be long before returns start rolling in. On the GOP side, caucusgoers will hear pitches from candidates or their representatives and then write their choice down in a secret ballot or vote with a show of hands.
Democrats, meanwhile, use a different system. Caucusgoers essentially gather together based on the candidate they are supporting.
But if a contender doesn't garner more than 15 percent of attendees, those people must go for their second choice. After a few rounds of balloting, candidates receive a proportion of the precinct vote.
Some candidates already are making deals to boost their numbers. Ohio Rep. Dennis Kucinich, for example, is unlikely to get more than the 15 percent threshold at many caucuses, so he has told his backers to unite behind Obama, giving him an edge over the other front-runners.
Tonight's caucuses will mark the beginning of the end of the most expensive, longest-running presidential campaign in American history, and help choose a successor to President Bush.
What is a caucus?
A party meeting at the precinct level at which voters express their candidate preferences and pick delegates to their county conventions. It's the lowest level of party politics - the real grass roots. These meetings, held in each of the state's nearly 1,800 precincts, typically draw anywhere from a handful of people in rural areas to hundreds in suburban areas.
Why is it politically significant?
Persuading a group of average residents to show up in support of a candidate is considered a sign of organizational strength. Each candidate courts politicians and activists at the state and local level in hopes of getting strong numbers of supporters to show up. At the same time, the caucus system allows candidates to develop and hone their message.