Great NPR article and video describing how the Iowa caucus is different than the primaries and other general elections...
What Goes On During the Iowa Caucuses, Anyway?
by Nancy Cook
The Iowa caucuses are not like the general elections, or even like primaries, where people declare their choices in a secret vote.
Iowans gather in their neighbors' homes, schools, churches or gyms for what's essentially a neighborhood party that lasts for hours.
Republicans choose their candidate based on a show of hands.
Democrats debate and try to build coalitions with other supporters from the same voting precincts. Democratic candidates need the support of at least 15 percent of each precinct to move on to the next round, the county convention. If a candidate is not deemed "viable" — if he or she cannot get the 15 percent — then their supporters are free to form coalitions with other candidates.
Interesting, isn't it? It's like old-fashioned elections.