The Iowa caucuses on Tuesday marks the beginning of the presidential nomination process for both the U.S. Republican and Democratic parties in the 2012 presidential election. Since President Barack Obama is running unopposed in the Democratic Party, all eyes are on the GOP race.

In the quadrennial U.S. presidential election year, the two parties officially nominate their respective candidate for presidency at their national conventions, to be held in the summer before the election in November.

The nomination is determined by the state-by-state primary elections spanning from start of the year to summer in the election year.

There are two forms of primary elections, namely caucuses and primaries. Caucuses gauge support for presidential candidates through local meetings of party members, while primaries gauge support through statewide direct voting. The events determine which candidates will receive a state's votes for the Republican and Democratic nominations at the parties' national conventions. The earlier a state holds the primary election, the more attention it receives from candidates and media.

For decades, the Iowa caucuses and New Hampshire primary has been running ahead of all other states, making them the place for candidates to "test the water" of the presidential election and to winnow the field. The results provide early indication of which candidates might win the nomination of their parties at the national conventions. The earlier the primary election date of a state, the more influential the turnout of this state is.

Historically, the Iowa caucuses are commonly recognized as the first major test of the U.S. presidential election year. This year's Iowa caucuses will be held on Tuesday when Iowans gather at a set location in each of Iowa's 1,784 precincts.

As a two-party State, Iowa is prone to neither the Democrats nor the Republicans, and the political environment there is more open and competitive. More importantly, Iowa is a small state, providing lesser known candidates a chance to win caucuses and march toward the White House, giving that these candidates may be less well-financed.

The Iowa caucuses do not result directly in national delegates for each candidate, and according to Professor Dennis Goldford at Drake University, a politics expert, it's more like a preference poll.

Caucus-goers elect delegates to county conventions, who elect delegates to district and state conventions where the national convention delegates are selected. A candidate who has the most number of supporters among elected national convention delegates in Iowa is considered winner of the caucuses in the state.