After months of hitting the campaign trail and fiery debates among presidential candidates, Monday will mark a permanent shift in the 2016 presidential race: actual voting.
The Iowa caucuses are significant because of their first-in-the-nation timing and their historic tradition. A good showing in Iowa is vital. No candidate that has finished worse than third has ever gone on to win the presidency.
But the Iowa contest isn't just your typical ballot-box election.
Iowa, unlike other early-voting states New Hampshire and South Carolina, does not operate as a traditional primary because they will not immediately award any delegates to a specific candidate.
Since 1972, Iowans have gathered in public places like schools and community centers not to elect delegates to the national convention like most other states, but to elect lower-level precinct delegates. These precinct delegates will go to one of 99 county-level conventions to advocate on behalf of the candidate they supported during one of the 1,681 precinct-level elections. From there, delegates are chosen for a congressional district-level caucus and finally a statewide convention, where delegates to the national convention are finally selected in late May.
Iowa Republicans and Iowa Democrats have different methods for electing their delegates. Iowa Republicans use a ballot system to elect their delegates; Iowa Democrats follow a more complex process. Democratic caucus-goers separate into small groups according to the candidate they support. If a candidate receives less than 15 percent support in the room, the candidate is eliminated and his or her supporters are then courted by the other groups.
The Iowa caucuses have a history of shutting down campaigns and giving candidates momentum. In 2004, former governor of Vermont and then Democratic frontrunner Howard Dean was expected to handily win Iowa. Instead, Dean finished in third place behind Massachusetts Sen. John Kerry and North Carolina Sen. John Edwards. Kerry's first place finish in Iowa revived his struggling campaign and propelled Kerry to win the New Hampshire primary and later the Democratic nomination.
Iowa also has a history of rejecting the frontrunners of each political party.
In 2008, then-Sen. Hillary Clinton lost the Iowa caucuses to then-Sen. Barack Obama. Pundits predicted that the Clinton campaign would lose the New Hampshire primary and then implode due to Obama's upset victory. Clinton was able to narrowly defeat Obama in New Hampshire and kept her campaign alive.
In 2012, former Pennsylvania Sen. Rick Santorum surprised the nation when he edged out former Massachusetts Gov. Mitt Romney in the Iowa caucuses by a razor-thin margin.
ABC's Chris Good contributed reporting.
Iowa Caucuses 2016: How the Caucuses Work