In days of yore, every state held causes, in which members of the various parties would gather to select delegates to go on to county conventions, then to state conventions and ultimately the National convention. 

That's essentially what's going on in Iowa tonight.  The Presidential preference portion really muddies this up.  But it also is a big attraction as it invites people who normally wouldn't care, even independents in to have their say about not only who the Party's nominee is, but also what potentially the State and National platform say. 

At least in theory, anyone who shows up and gets themselves selected as a delegate can go on to the State or National convention and actually have one of those BIG, COUNTING votes for the party's nomination.

Contrast this to a Primary state, which is more like the Electoral College.  You vote your preferences, but the Party gets to decide who gets to go to the State and National conventions.  According to each state's party rules, the delegates need not even be BOUND to the candidates you select!

Now to the presidential prefernce part. Iowa is divided into precincts.  Each precint is given a certain number of delegates based upon the number of residents in that precinct.  It doesn't matter how many people show up to your individual precinct.  If more people show up, your individual vote counts less.  If less, your vote counts more.

Everyone divides up into groups supporting their candidate or "Undecided." (Believe it or not Undecided WON the Democratic Iowa Caucuses in 1976.)  You take the total number of people there and divide by the number of assigned delegates.

So you're going to have TWO results tonight.  First the HEAD COUNT, the  preferences of all the participants, including Undecided.  And the Delegate count. 

I attended the Iowa Caucuses in 1988.  There were ~147 participants, representing about 1500 people which had 21 assigned delegates. So that's 7 people per delegate.  We then arranged ourselves in clumps of seven or multiples of seven.  Each seven gets to select a delegate.

Then comes the 15% Viability Test.  (This is just on the Democratic Side.)  You must have at least 15% of the goers present in your precinct in order to have any delegates pledged to your candidate at all. 

If a candidate is not viable they have to convince people from other camps to come over.  Perhaps the Richardson and Biden camps could combine to make a viable camp.  However, that camp would have to choose whether to be Nominally Richardson or Biden. 

You don't get 1/2 votes.  If say, in my precint, a candidate hade 24 goers, that's 3 delegates, not 3 1/2.  You have to try to pursuade 4 more into your camp for your fourth delegate.

So, let's say there are 7 goers per delegate and Obama has 27.  Suddenly, far from being the loneliest person in the building, the lone KUCINICH person in the room has the POWER to offer himself to become an Obama person in exchange for getting to become a delegate in the next round. 

That person would nominally be Obama, for purposes of the Delegate count, but would be free to vote Kucinich in the next round.  More importantly, that person would probably be a strong anti-war delegate and get to push that issue in higher conventions.

Or you can BARGAIN and give your SPARE goers over to another camp.  So, say if Hillary had three exttra goers and no one will join her camp to give Hillary another delegate, they could join the Richardson camp to make it viable.  In exchange one of their delegates would be, again, NOMINALLY Richardson, but free to vote Hillary in the higher rounds.

So there's all sorts of ways the Caucuses can play out.  People with Unviable candidates can slink on over to their second choice or drive hard bargains to force representation in the next round.  Front runners have to choose whether they want to play for TONIGHT or log-term  Do they give up Nominal delegates to other camps in order to get more of their people into the next levels?  Or do they allow people whose first preference is NOT their candidate in order to get one more Nominal delegate for their candidate TONIGHT?