Brace yourself. That annual red-carpet cavalcade of media preening and zeitgeist chasing known as the White House Correspondents’ Association Dinner hits Washington this week. And right now you’re wondering:

What exactly is this thing, anyway? And can I go?

We’ll take your second question first. No. Unless you are a very important Washington player or corporate titan, it’s next to impossible. Don’t bother asking your journalist friends: They’re probably not in either, unless they cover the White House or politics. Saturday’s event is about as elite as a dinner for 3,000 can be.

But what IS it?

Originally, just the equivalent of an annual professional association dinner — except that the professionals in question are White House reporters and the annual guest of honor, delivering a comedic speech, is the president.

So what are celebrities doing there?

Good question! As far back as the 1920s, it always had a bit of glitz, with showbiz stars hired to perform. (This year, Conan O’Brien will serve as the after-dinner jokester.) But the invited guests were generally somber Washington types whom journalists hoped to cultivate as sources. That began to change in 1987, when the late Michael Kelly brought Iran-Contra “it girl” Fawn Hall as his guest; the next year it was Gary Hart scandal lady Donna Rice. Both were arguably newsmakers — but they caused such a sensation that soon media organizations were clamoring to find the buzziest guests. That’s led to the current situation where planeloads of Hollywood luminaries or sports stars are shipped in — increasingly crowding actual reporters out of the dinner seats, so that media bosses can impress the advertisers and bigwigs sharing their tables. (Update, 2 p.m. Monday: After a long absence, Barbra Streisand will be attending the WHCA dinner this year.)

Do Elizabeth Banks and John Legend have lifetime passes or something?

Media types used to look for novelty in their guests, but lately, some well-behaved stars appealing to certain yuppie tastes seem to get invited back year after year.

But it’s not just the dinner, right?

Indeed. As the WHCA dinner evolved into more of a national happening, the pre- and post-parties have proliferated, sprawling out over a period of five days. Most are hosted by individual media organizations seeking to promote their brand and entertain their high-profile out-of-towners.

What’s the best party?

The Bloomberg/Vanity Fair Saturday night after-party has long been the most chic and lavish by far. But with the density of A-listers, it’s become almost too elite for local party animals to aspire to — virtually crash-proof, and it’s not like any of your friends will be there anyway. That’s helped MSNBC’s second-banana after-party — a big, lively affair with a dance floor — grow in popularity. (Although you probably can’t get in there either anyway.)

Is this really an appropriate time to party?

We’ll see. Dinners are often subdued by current events. In 2003, President Bush skipped the jokes to honor journalists Kelly and David Bloom, both of whom died covering the Iraq war; he also took a pass in 2007, when the dinner fell days after the Virginia Tech shootings.

Amy Poehler arrives at the 2009 dinner. (Lois Raimondo / The Washington Post)

Best place for star-gazing?

You can watch VIP guests arrive at the Washington Hilton.