Clint Eastwood once said that there were only two American art forms: jazz and the Western. But he could well have added another: the late-night talk show.
From the early days of The Ed Sullivan Show and The Tonight Show through to current series like Late Night With Jimmy Fallon and Conan, the late-night talk show is an American institution. And one of its longest-running proponents is the marvellous David Letterman.
With its house band, celebrity guests and opening monologue from its laconic host, the nearest equivalent we've ever had in Britain is probably Jonathan Ross's chat shows - notably, his late '80s show for Channel 4, The Last Resort with Jonathan Ross - but still, no one's quite come close. And certainly not for so long.
So, with the news that our very own David Cameron is appearing on Dave's show*, we thought we should do a little beginner's guide for our Prime Minister, his aides, and anyone else who's new to the show:
Top 10 Things To Know About Late Show With David Letterman
1. Each show features a 'Top 10' list
Like this, only funnier. From Top 10 George Bush Moments to Top 10 Things That Sound Cool When Said By Snoop Dogg, the lists originally started as a mickey-take of People magazine's weekly Top 10 lists - a fact reflected in the very first one, which was 'The Top Ten Things That Almost Rhyme With Peas'.
2. The show is recorded at the Ed Sullivan Theater in midtown Manhattan, New York
Letterman and his crew work four days a week, taping Friday's show earlier in the week.
3. The house band is called the CBS Orchestra
And it's led by Paul Shaffer, who's been at Letterman's side since 1982. It was also previously the house band of Late Night With David Letterman (minus the horn section), when it was known as The World's Most Dangerous Band.
4. As well as the opening monologue, guests and music, the shows often feature sketches, stunts and running gags
5. Drew Barrymore flashed her boobs at Letterman in "a birthday gift he'll never forget"
We don't recommend that Cameron does this.
6. The 1994 episode featuring Madonna as a guest is the most censored in American talk-show history
Why? Because Madge said the word "fuck" thirteen times. Again, we don't recommend that Cameron does this.
7. Sarah Palin doesn't like David Letterman
8. Letterman didn't miss a single day's recording for 18 years
His excuse for finally pulling a sickie? A quintuple heart bypass (in January 2000).
9. It's won the 'Outstanding Variety, Music or Comedy Series' Emmy Award six times
And was nominated for sixteen years in a row from 1993.
*10. It's OK to call David Letterman 'Dave'
Everyone does. Although if the Prime Minister tries it, we'll probably cringe.