Primary matters: how the major parties choose their candidates.

• Position: Upfront: ELECTION 2016

After almost a year of polls and speculation about the 2016 presidential election, the actual voting begins next month with the Iowa caucuses on February 1 and the New Hampshire primary on February 9. With so many contenders still in the race--3 Democrats and 14 Republicans at press time--it's unclear at this point whether nominees for each party will emerge quickly, or if the battle will continue into the spring or even until the parties' conventions in July.

How did this system come about?

In the 19th and early 20th centuries, elected officials and party leaders chose presidential candidates at the conventions. Progressives began promoting primaries--elections to choose party nominees--in the late 1800s, saying party bosses were cutting backroom deals to select nominees. The first primaries occurred in the early 1900s, but it wasn't until after World War II that they began to play a significant role in choosing candidates.

What are the primaries about?

A primary works very much like a general election. On dates selected by each state (see map), voters head to polling places to cast secret ballots. Based on the results, the state parties allocate delegates for each candidate to the national convention, where the presidential nominee is formally chosen. At the Republican convention, the winner needs a majority of the approximately 2,400 delegates; the Democratic nominee will need a majority of the approximately 4,000 delegates.

How are caucuses different?

Some states, like Iowa, have caucuses rather than primaries. In caucuses, party members meet at the district or precinct level--gathering at schools, churches, and even private homes--to discuss the candidates and the issues. Then they publicly declare who they're supporting. Iowa has more than 1,700 precincts, each hosting its own caucus.

What's the role of the conventions?

In most recent presidential elections, a candidate from each party has collected enough delegates in the primaries to all but guarantee the nomination. This has turned the conventions into little more than three-day-long TV ads for the candidates, since the actual tallying of votes is just a formality. But a tight race on the Republican side in 2016 could lead to a convention fight, which last happened in 1976, when President Gerald Ford narrowly beat Ronald Reagan to win the Republican nomination. Why are Iowa and New Hampshire so important?

In a word: tradition. Since 1952, the New Hampshire primary has been the...