Four years ago in Boston, a little-known senator from Illinois made his debut on the national stage with a stirring keynote speech at the Democratic National Convention. This year, that senator, Barack Obama, will again give a pivotal speech at the DNC, but this time he'll be the headliner and his speech will be a historic acceptance of the Democratic nomination for the presidency.

More than 50,000 people will attend the convention — including 5,000 delegates and 15,000 reporters — which will take place Monday (August 25) through Thursday at Denver's Pepsi Center. The convention will be capped on Thursday by Obama's eagerly anticipated speech in front of 75,000 at INVESCO Field at Mile High during a free event open to the public.

Thursday will mark the first time since John F. Kennedy's 1960 address at Los Angeles' Memorial Coliseum that a Democratic nominee has given his acceptance speech outside the convention's main floor. Given the image of youth and change that Obama has cultivated during the campaign season, the allusion to Democratic history is clearly intended to tug on heartstrings. The speech will also coincide with the 45th anniversary of civil rights leader Dr. Martin Luther King Jr.'s "I Have a Dream" speech, another bit of serendipity that provides further emotional resonance for the man who has made history as the first black presidential nominee of either major political party.

But just what is the purpose of the gathering, and why are Democrats spending a reported $40 million-plus on the event? Some facts about the convention:

» Delegates from each of the 50 states meet at the Democratic National Convention every four years to select the Democratic candidates for president and vice president.

» The event, which typically takes place in a major city such as Chicago (11 times), Baltimore (eight) or New York (five), is not open to the public, but only to delegates, the press, party members and other invited guests. The Denver convention will take place on the 100th anniversary of the party's 1908 convention in that city.

» A complicated formula is used to determine how many delegates are invited from each state, using the number of votes cast in the past three elections. It looks something like this: (State's Democratic Vote/Total Democratic Vote) + (State's Electoral Vote/Total Electoral Vote)/ 2 X 3,000 = # of Delegates Per State. The formula ensures that heavily Democratic states have a higher number of delegates. Organizers expect 4,440 delegates to attend, with 4,235 casting votes.

» Thanks to his lead in elected delegates and superdelegates, Obama is expected to receive the nomination. Democratic Representative Loretta Sanchez, however, predicted that half of the Democrats in the House could cast their votes for Obama's former rival for the nomination, Senator Hillary Clinton. The Obama campaign has agreed to allow a floor vote at the convention to assuage Clinton supporters, though even Clinton has said she plans to vote for Obama.

» Delegates are not paid for their participation, and most will come at their own expense after being selected on a statewide level in a sometimes complicated process that involves some politicking of its own. Some as young as 19 will be participating for the first time alongside party veterans. The youngest delegate is Minnesota's David Gilbert-Pederson, 17, who is one of two delegates under 18 expected at the event; almost 15 percent of the delegates are 36 years old or younger.

» The incumbent party traditionally holds its convention after the challenging party's. The Republican convention will take place in Minneapolis-St. Paul during the first week of September. The conventions were pushed back this year due to the Olympics.

» House Speaker Nancy Pelosi will be nominated to chair the convention, whose first day's theme will be "One Nation." On Monday's schedule: an address from Michelle Obama and a tribute to Senator Ted Kennedy.

» After a bruising primary season in which Senator Obama ran neck-and-neck with Senator Clinton, Democrats faced the possibility of a brokered convention, during which the nominee would not have been chosen until a vote at the convention. But that potentially divisive option was avoided when Clinton conceded the race to Obama.

» Michigan and Florida had their delegate votes docked for moving their primaries to January, but after much wrangling and back-and-forth, the two states were granted half-votes each at the convention.

» Tuesday's speakers include Governor Kathleen Sebelius of Kansas, Governor Janet Napolitano of Arizona and Governor Deval Patrick of Massachusetts, all of whom had generated buzz as potential running mates. The theme is "Renewing America's Promise," and the keynote speaker will be former Virginia Governor Mark Warner. Senator Clinton will also give a speech during prime time, and the party's proposed national platform will be discussed and debated.

» Wednesday's theme is "Securing America's Future." Former President Bill Clinton will address the convention, as will vice presidential candidate Joe Biden. Former presidential candidate Bill Richardson is also among the speakers, as well as 2004 Democratic presidential candidate John Kerry.

» The final day's theme is "Change You Can Believe In." Obama will deliver his speech that evening.

» According to the DNC, California will have the biggest delegation at 503, with American Samoa pulling up the rear with 13 delegates. Journalists from more than 130 nations will converge on the event.

» Some terms you might hear during the convention:

At-Large Delegate: These are pledged delegates who are the very last to be elected on a statewide level and represent presidential candidates in proportion to the statewide vote the candidate received in the primary or caucus.

Credentials Committee: This group resolves any disputes over the seating of delegates and alternates to the convention.

Platform: This is the official statement of the party's position on a variety of important issues. Each issue included in the platform is called a "plank."

The convention won't be all politicians and funny hats, though. According to the New York Daily News there will be serious star power on-hand as well, including possible appearances by George Clooney, Madonna, Kanye West, Scarlett Johansson, Susan Sarandon, Spike Lee, Quentin Tarantino and Matt Damon.

James Taylor and Tony Bennett are performing at a fundraiser for Pelosi during the event, and Kanye West is reportedly hosting a gig in honor of the Recording Industry Association of America. Among the stars that could make appearances are Annette Bening and hubby Warren Beatty, Matthew Modine and Kerry Washington.

Rock the Vote will hold an event called the Ballot Bash during the first night of the convention; it will feature sets from Fall Out Boy, N.E.R.D. and Jakob Dylan, with an afterparty DJ'd by Nick Cannon. In addition, Rage Against the Machine will be playing a gig during the DNC — as well as during the Republican convention the following week — as part of a larger protest called the "Tent State Music Festival to End the War." Daughtry, Everclear and the Flobots will play a show sponsored by the Grammy Foundation during the DNC as well. Other acts playing during the convention include Death Cab for Cutie, Cold War Kids and Moby.