Click here for the final results and analysis.

Update, 1:40 a.m.: Now Romney is ahead by one vote. One single vote. Still waiting on one or two precincts.

Update, 12:36 a.m.: Santorum back ahead by 5 votes, with 99 percent of precincts reporting. Five votes. No joke.

Update, 12:25 a.m.: With 98 percent of precincts reporting, Romney has snatched the lead from Santorum by 41 votes. What a race.

Update, 12:11 a.m.: A breaking-news alert from The New York Times says Rick Perry is heading back to Texas to assess his campaign's future. No further details are available at the moment.

Update, 12:07 a.m.: This race is closer than Florida in 2000. With 97 percent of precincts reporting, Santorum is in first place and Romney in second -- but just 37 votes separate them. Ron Paul is in third by just under 4,000 votes. The fortunes of the also-rans have not changed much since earlier in the evening: Gingrich has 13.3 percent, Perry has 10.3 percent, Bachmann has 5 percent and Huntsman has 0.6 percent. According to state Republican officials, there will be no recount no matter how close it is. Check back for a full analysis of the results once the last 3 percent of precincts report.

Update, 10:52 p.m.: Results are pouring in now, and it doesn't look good for Paul. With 88 percent of precincts reporting, Santorum leads Romney by just 45 votes, but Paul trails by more than 3,500. It's 24.6 percent for Santorum, 24.5 percent for Romney and 21.1 percent for Paul.

Update, 10:43 p.m.: With 59 percent of precincts reporting, the order is still Santorum, Romney, Paul, and still very close: the difference between first and third place is 2.8 percent. And as Washington Post blogger Aaron Blake tweeted a few minutes ago, Paul will probably improve his standing as the night goes on: For those counting out Paul, just remember: no votes counted yet from counties that are home to Iowa State and University of Iowa.

Update, 10:08 p.m.: The order is now Santorum, Romney, Paul. Santorum and Romney are just 246 votes apart, and Paul is 1,077 votes back out of a total of 54,223 votes cast, with 47 percent of precincts reporting.

Update, 9:45 p.m.: With 31 percent of precincts reporting, the order of the leaders has changed: Romney is now in first, Santorum in second and Paul in third, but the margins are infinitesimal: just 0.6 percent separates the three of them. Expect this dead heat to continue for most of the evening.

The second tier remains the same, with Gingrich in fourth place, followed by Perry, Bachmann and Huntsman.

--

The night is young, but with 26 percent of precincts reporting, the results of the Iowa caucuses look very similar to pre-caucus polls.

Ron Paul is leading with 23.1 percent of the vote, but Mitt Romney and Rick Santorum are close behind with 22.9 percent each. After that, there is a significant drop-off from the first tier of candidates to the rest of the field: Newt Gingrich has 13.2 percent, Rick Perry has 10.4 percent, Michele Bachmann has 5.9 percent and Jon Huntsman has 0.6 percent.

The percentages were slightly different in the last Des Moines Register poll conducted before the caucuses, but the order was much the same, with Paul, Romney and Santorum bunched at the top, followed by Gingrich, Perry, Bachmann and Huntsman, in that order.

The results are not identical to the poll, however: The order of the three top candidates has changed, although they remain too close to say who will be on top once all the votes are counted. The poll showed Romney in first, Paul in second and Santorum in third, while the early returns show Paul in first and Romney and Santorum tied for second. We will see in the coming hours if that order holds.

If it does, Santorum will have beaten expectations by an even larger margin than it seemed like he would in the final days of the campaign. Even third place would be a huge upset for him, given that just a week ago, he was polling sixth out of seven candidates. For his supporters, a second-place finish would exceed not just expectations, but dreams -- and for Romney, finishing tied with or behind a former cellar-dweller like Santorum would be tremendously embarrassing, even if it did not derail his campaign.

Check back for updated results and analysis throughout the evening.