A primary election is a preliminary election that is held to determine which candidate will receive the nomination of his party to represent them in a general election. The winning candidate then runs in the nationwide general election against the candidate nominated by the other party or parties.
Originally, caucuses (a meeting of members or supporters of a political party) were the main method used to select candidates. The primary election developed from a move in the 20th century to give citizens more power in the selection of the candidate for their party. For the first time, registered voters were allowed to choose the candidate by voting through secret ballot, just like in the general election.
The two main types of primaries are open or closed, with each state determining the type of primary it will hold. In a closed primary, a registered voter can only vote in the election held by the party she is registered with. For example, a registered Democrat would only be able to vote in the Democratic primary, and a registered Republican could only vote in the Republican primary. In an open primary, a registered voter can vote in either party's primary, regardless of affiliation.
Each state decides if and when it will hold a primary election. Some states hold their primary early in the process, and in many cases, the candidates are chosen after only a few state elections. The voting process is very similar to that of a general election. Registered voters place their vote by secret ballot at their designated polling place. The Republican Party allows each state to decide whether caucus participants or the number of primary votes received determines which candidate is awarded the delegates for that state. The Democratic Party uses the proportional method for awarding delegates, which means the percentage of delegates awarded to each candidate is represented by the number of primary votes received. Once a candidate is awarded the required number of delegates, the candidate unofficially becomes the nominee of his party.
After the caucuses and primaries are over, each party holds a national convention. At the convention, a group of delegates vote state-by-state for their candidate. Each delegate is chosen at the state level, prior to the convention. At the end of the convention, each party formally announces who its candidate will be. The end of the convention signals the official beginning of the general election.