For great American traditions, you can't beat the hoopla of big political conventions. This week in Boston, the Democrats are getting together. Next month, the Republicans will gather in New York.

Held in vast arenas draped with red-white-and-blue bunting, the conventions are a cross between a big sporting event and a Fourth of July celebration. The grand finale comes when the candidates for president and vice president, officially approved by the delegates at the convention, march on stage. Music blares. The candidates link their arms and pump them skyward. Supporters yell as thousands of balloons rain down.

These things about conventions haven't changed.

But most things have.

When they began in the 1830s, the main purpose of conventions was to choose presidential candidates. In 1924, the delegates to the Democratic convention had to vote 103 times before nominating John W. Davis for president. Before 1932, the candidates didn't even go to the convention. Franklin D. Roosevelt was the first candidate to accept the nomination in person.

Now, by the time the conventions are held, the voters for each party have made that choice in primary elections and caucuses.

Ordinary people, rather than political party leaders, now have the greatest voice in choosing candidates.

In the past, at least some important decisions were announced at the conventions. In 1960, for example, the public did not know who John F. Kennedy would choose to be his vice president until the convention began. He selected Lyndon B. Johnson.

Everyone has known for weeks that Sen. John Kerry picked Sen. John Edwards to be his running mate and for months that Vice President Cheney would run with President Bush.

For many years, much of the convention's business was done behind closed doors. Now, the doors are open and parties and politicians are desperate for the public to watch. There will be roughly 15,000 news people at the conventions and only about 4,000 delegates and alternate delegates.

"The conventions provide the candidates with one of the best opportunities during the whole campaign . . . to give people an idea of what they would do if they are elected," says Washington Post political writer Dan Balz.

Conventions today are all about getting voters to decide to vote for their candidate. To do that, parties plan conventions carefully so that everything looks nice to the voters. It's like cleaning your room before company comes.

Conventions haven't always been happy, family-reunion affairs though. In 1968, anti-Vietnam War demonstrators outside the Democratic convention in Chicago fought with police while delegates inside started shouting at each other.

Still conventions do get people to pay attention to politics, politicians and issues. If you watch this year's conventions, you might see a politician you've never heard of giving a speech. In a few years, that person might be running for president. In 1988, a little-known governor from the South gave a speech at the Democratic National Convention. It turned out to be a terrible speech. The governor was teased by late-night comedians for days. His name was Bill Clinton.

In the end, the convention is really about showing off the candidates for president and vice president.

When these men (and with the exception of Geraldine Ferraro, who was Walter Mondale's running mate in 1984, they've all been men), give their acceptance speeches, it's the first time many people actually begin thinking about how they might vote. And that's probably a good reason to check out the conventions -- that and to see who is wearing the goofiest hat.

-- Fred Barbash