What is the Iowa caucus? It’s the gathering of individuals to discuss policies and express preferences about candidates for the presidential election. People meet in schools, libraries, churches or individual homes. Anyone who will be 18 by the time of the presidential election can attend, although you usually have to register with the relevant party to participate. At Republican caucuses, each person simply picks the candidate they favour. At Democrat caucuses, people split into groups supporting the various candidates. If a candidate fails to get 15% of the total, those people must realign with another candidate. The popularity of candidates determines how many delegates they are allocated to attend the parties’ national conventions, which choose the final presidential candidates

How does it differ from a primary? In a primary there is a more straightforward and secret vote on potential presidential candidates. At an ‘open’ primary, anyone can vote for any candidate; at a ‘closed’ primary, only registered party members can vote in each of the party contests

Why does Iowa have a caucus and New Hampshire a primary? Both states have a tradition of being first out of the blocks in the presidential race, and kept seeking to move their dates forward. So in the 1980s they struck a deal: Iowa would hold the first caucus and New Hampshire the first primary

How does the electoral process then unfold? Each state holds a primary or caucus, which decides the delegates to be sent to county conventions and then the national conventions of both Democrats and Republicans. Super Tuesday is the name given to the day on which a large number of states hold primaries or caucuses. In 2008 it will fall on February 5, when 25 states will take part. In the summer the Republicans and Democrats hold national conventions to endorse one candidate as their nominee for the presidential election. The frontrunner, however, may have become clear well in advance

What happened after previous Iowa caucus results? Since 1972, the final nominee for both Republicans and Democrats has always been among the top three candidates in the Iowa caucuses. In 2000 George W Bush won the Republican race and went on to win the presidency. In 2004 John Kerry, who became the Democrat challenger, won in Iowa and became the Democrat candidate, only to lose the presidential election to Bush

Times Recommends

• 'New York has lost its edge'
• Copenhagen will fail – and quite right too
• More than 17,000 new underwater species found