If you live in Ohio, you'll be hearing a lot from John Kerry and George W. Bush in the coming months -- television commercials, personal appearances and juicy campaign promises galore. It's a swing state, after all.

No such luck if you live in nearby Illinois, a state that most observers predict Kerry will win handily. There, you should be glad if the candidates touch down to refuel.

Swing states -- that is, states that both candidates have a chance at winning -- are the real battlegrounds in this election, especially given the winner-take-all Electoral College system in which the leading vote-getter in a state wins all the state's electoral votes. Whoever wins Ohio, for example, receives 20 electoral votes, whether he wins the state by one vote or a million votes. Given this system, both candidates will spend most of their time battling to win voters in states where the race is likely to be close, rather than voters in states like Illinois, where the outcome is less in doubt.

All states, in fact, can be divided into three categories: those that will almost certainly vote for Kerry, those that will almost certainly vote for Bush, and swing states that may go either way. It takes 270 electoral votes to win the presidency and both campaigns have mapped out a strategy for winning just enough states to top that mark. President Bush, for example, expects to win a number of states -- Texas (34 electoral votes), Georgia (15), Wyoming (3) and perhaps 15 others. Similarly, Kerry is counting on winning in Massachusetts (12), New York (31), Illinois (21) -- perhaps 10 states in all.

That leaves 22 states -- the swing states -- that will determine the next president. Want a list? If you live in Arizona, Arkansas, Colorado, Delaware, Florida, Iowa, Louisiana, Maine, Michigan, Minnesota, Missouri, Nevada, New Hampshire, New Jersey, New Mexico, Ohio, Oregon, Pennsylvania, Tennessee, Washington, West Virginia or Wisconsin, you might live in a swing state.

Voters in these states can expect a barrage of campaign ads, frequent visits by the candidates, and perhaps most importantly, a campaign message designed to appeal especially to them. For example, some say that President Bush's recent restrictions on travel and transferring funds to Cuba was done in large part to appeal to the numerous Cuban-American voters in the swing state of Florida. Similarly, John Kerry's selection of a vice president may hinge on whether that person will help him win a swing state or two.

Does all this attention mean that votes from swing states count more? In a sense, yes. Each individual vote in a state with a neck-and-neck race is more likely to be the deciding vote and, given the Electoral College system, the deciding vote in one state could be the deciding vote nationwide.

There is no better example of this than Florida in 2000, where, according to the Supreme Court, 537 people were the deciding vote for the nation. Those 537 votes (out of 5.8 million votes cast) gained all 25 electoral votes for George W. Bush and led to his 271-267 victory in the Electoral College, despite the fact that Al Gore received 500,000 more votes nationwide than Bush. If 600 more Floridans had cast a vote for Gore that day, the country would have elected a different president. Contrast Florida to California, a state Gore won by 1.3 million votes: If 600 more Democrats had gone to the polls in that state, nobody would have noticed.

The good news for voters in California is that presidential elections don't usually come down to a handful of voters in Florida or any other single swing state. Depending on the mood of the nation, the majority of swing states tend to break for one candidate or the other -- from 1980 through 1996, for example, whoever won the big swing states of Pennsylvania, Michigan, Missouri, and Ohio won a majority of the other states, as well as the presidency. But if history repeats itself and this election comes down to 500 votes in Ohio or any other swing state, both Bush and Kerry hope the hundreds of millions of dollars they poured into campaigning in those states will be enough.