Beginning at 7 p.m. Central on Monday, Democrats and Republicans in Iowa will be the first in the country to select their preferences for their parties' respective presidential nominees in 2016 (the full process is a bit more complicated).
On the Republican side, frontrunner Donald Trump held a promising — some would say tremendous — lead in polls over a veritable circus of rivals. Their ranks include Texas Sen. Ted Cruz, Florida Sen. Marco Rubio, retired neurosurgeon Ben Carson, Kentucky Sen. Rand Paul, former Florida Gov. Jeb Bush, former Arkansas Gov. Mike Huckabee, Ohio Gov. John Kasich and New Jersey Gov. Chris Christie bringing up the rear alongside former Hewlett-Packard CEO Carly Fiorina.
The Democratic field is less crowded, with caucus-goers choosing between just three candidates: former Secretary of State Hillary Clinton, self-declared democratic socialist and Vermont Sen. Bernie Sanders and former Maryland Gov. Martin O'Malley. The race largely comes down to a close contest between Sanders and Clinton, with O'Malley a distant third.
Anything can and does happen in Iowa, which has ruined and raised presidential ambitions before. The maps below will automatically refresh with county-level votes as they come in.
This post will be continually updated with live coverage of the caucuses as the results start to come in (all time stamps are in eastern time).
12:45 a.m.: The final tally in the Iowa caucus has come to a Democratic tie and a victory in the Republican race for Ted Cruz.
Hours after Iowans were done caucusing, the Democratic tally stood slightly in Clinton's favor, but was too close to call. With 96% of precincts reporting, Clinton led Sanders 49.9% to 49.6%.
In the Republican race, Cruz pulled off a solid victory, totaling about 27.6% of the final vote. He placed above Trump at 24.3%, Rubio at 23.1% and Carson at 9.3%. Bush, once widely hailed as the probable nominee, ended in a dismal sixth place at 2.8%, behind Paul, who received 4.5%.
12:19 a.m.: Sanders declares his "political revolution" far from over and vows to continue fighting in fiery speech.
Sanders said his campaign had sent a "very profound message to the political establishment," as well as power brokers in the economy and media.
According to ABC's MaryAlice Parks, the Sanders campaign is characterizing the candidate's speech as a victory one — sort of.
11:52 p.m.: Clinton claims victory, though it's unclear who actually won yet.
"As I stand here tonight, breathing a big sigh of relief, thank you, Iowa," Clinton told supporters."Think hard about what the Democratic Party looks like and what we want the future of our country to look like if we do our part to build it. I am a progressive who gets things done for people."
She added she will be a strong advocate for "Women's rights, gay rights, voting rights, immigrant rights."
As of 11:51 p.m., more than 20 minutes after the beginning of Clinton's speech, the outcome of the race remained unclear. With 94% of precincts reporting, Clinton and Sanders were virtually tied at 49.9% to 49.6%.
11:38 p.m: In victory speech, Cruz thanks God and tells audience his victory defied media projections.
"Let me first of all say, to God be the glory," Cruz told assembled reporters. "Tonight is a victory for the grassroots. Tonight is a victory for courageous conservatives across Iowa and all across this great nation."
"We together earned the vote of 48,608 Iowans. To put this in perspective, your incredible victory that you have won tonight, that is the most votes ever cast for any Republican primary winner" in Iowa, Cruz said.
11:04 p.m.: A humbled Trump, having placed over 3% behind Cruz, acknowledges loss in speech to Iowans.
Trump said that he was "honored" to have placed so well in Iowa, telling members of his party he will continue the fight in the second primary state of New Hampshire.
"We're gonna be in New Hampshire. It's gonna be a great week," Trump said.
In one of the more memorable moments of the night, Trump even told Iowans he might purchase some land in the Hawkeye State.
"We will be back many, many times — in fact, I think I might come here and buy a farm," he added.
10:41 p.m.: With results still rolling in, Sanders is now closer to Clinton than all the people who chose Martin O'Malley put together.
10:38 p.m.: Rubio is clearly pleased with his performance in Iowa tonight.
10:28 p.m.: Huckabee just dropped out of the race.
10:26 p.m.: Multiple news agencies are calling the Iowa race for Cruz.
10:24 p.m.: Trump is on the way to placing third, behind both Cruz and Rubio.
This isn't going the way Team Trump hoped it would. With 83% of precincts reporting, Trump polls at 24%, behind Cruz at 27.7%. More alarmingly for the real-estate billionaire's presidential prospects, Rubio could now conceivably place him in third — he's gaining on Trump, with 23% support.
10:14 p.m.: The Democratic race is too close to call, even as it races towards a conclusion.
70% of precincts have reported results, and Sanders is edging closer and closer toward Clinton. Approximately 49% of Democrats have sided with the democratic socialist from Vermont, and just 50.4% have sided with Clinton.
10:05 p.m.: Martin O'Malley, faced with the prospect of 0% support in tonight's caucus, will reportedly drop out of the race later tonight.
O'Malley will suspend campaign operations after facing a shellacking in Iowa. According to the New York Times, in the city of Indianola, the governor from Maryland struggled to secure even a single delegate.
10:04 p.m.: High turnout, originally expected to help Trump, appears to actually be hurting him.
Analysts originally expected that low turnout would favor Trump's opponents, particularly Ted Cruz. But record turnout is being reported across the state, with Politico estimating over 170,000 Republican participants, up from 121,000 in 2012. As Trump continues to lag behind Cruz, and Rubio outperforming expectations, some analysts are concluding that large numbers of people went to the polls specifically to vote against Trump.
9:49 p.m.: Trump is still trailing Cruz by over three percent, even as the results add up.
This has been a tough night for Trump so far. He's been performing well under what pre-caucus polling would suggest all night, and now, with 56% of precincts posting results, he trails Cruz 28.7% to 25.1%.
9:38 p.m.: A Democratic voter just dropped the F-bomb on live television, calling the Department of Veterans Affairs "fucked up" on an MSNBC broadcast.
9:35 p.m.: With over half of Democratic precincts now reporting, Sanders is narrowing the gap, but remains behind Clinton.
With 61% of precincts now reporting results, the race for the Democratic nomination remains very close. Clinton has 50.9% of the vote, while Sanders has slightly closed the gap at 48.5%.
9:12 p.m.: With more precincts reporting, Clinton and Cruz maintain early leads.
With a full 26% of precincts reporting, Clinton maintains a strong lead over Sanders, 52.6% to 47%.
Republican precincts are reporting more slowly, but with 5% reporting, Cruz is holding a 30.1% to Trump's 28.8%.
8:54 p.m.: There are more Republicans voting for the first time than in 2012, and they lean toward Trump by double-digits.
8:46 p.m.: The first results are trickling in.
With 9% of Democratic precincts reporting, Clinton leads Sanders 53.3% to 46.0%.
Just 2% of Republican precincts reporting, Cruz has an early but razor-thin lead over Trump, 32.6% to 32%, with Rubio at a distant 14.3%.
8:31 p.m.: Iowa Democrats caucusing for the first time favor Sanders by large margins
8:11 p.m.: Time reports only 11% of respondents in a CBS News exit poll who chose a candidate "in the last few days" chose Trump.
8:10 p.m.: Ben Carson will take a break for "R&R" after Iowa, going to Florida instead of New Hampshire or South Carolina.
According to CNN Politics' Chris Moody, Carson — who has plummeted in the polls following a brief surge in fall 2015 — will not be sticking around in Iowa for very long tonight.
In fact, Carson will likely be catching a plane out of the state before the results are even in, and instead of heading early to the next important primary contest in the state of New Hampshire, will be heading to Florida for a vacation from the campaign trail.
Campaign officials told PBS' Lisa Desjardins that Carson's campaign schedule was still on track, but he just needed more clothes: