With the success of "The Office," "Borat," "Talladega Nights" and other recent hits, it's hard to ignore improvisational comedy. The word "improv" not only gets as many projects greenlit these days as "Spielberg," but it also connotes mysterious images of comedians working with no net, screenwriters banned from the set and pop-culture-catchphrases dropping from the sky like tender snow-farts.

But what exactly is improv comedy? How long has it been around? And who's the best at it? We asked the world's funniest people those very questions and found that -- much like takes on a Judd Apatow movie -- no two responses were alike.

"We made up all our lines," Seth Rogen remembered of Apatow's 2005 flick, "The 40-Year-Old-Virgin." "A lot of the stuff was just us talking to each other and trying to make each other laugh, knowing that we had the freedom to say whatever we wanted. It looks very natural, because we honestly didn't know what we were saying until we were saying it."

When Will Ferrell surrounds himself with people like Steve Carell and Paul Rudd, improv is "the stuff that happens constantly," he said. "Even though [so much of] it won't make it into the movie, it's that kind of spirit that's contagious."

Mike Myers offered a similar definition: "What you can't fix, you feature, and mistakes are great happy accidents. That's the essence of improv, and movies are so chaotic, they're like a runaway train. You have to have that mentality, or the train leaves without you."

Of course, Christopher Guest has practically made a directing career out of largely improvised films like "Waiting for Guffman," "Best in Show" and, most recently, last year's "For Your Consideration." And he, along with Michael McKean and Harry Shearer, comprise Spinal Tap, the fake band that was presented mockumentary-style in the landmark comedy flick "This Is Spinal Tap."

The goal for such films -- and TV shows like "Reno 911!" -- is to ditch contrivances, such as the goofy next-door neighbor, and instead capture a funnier version of real life. "It's the next best thing to reality TV," added "Virgin" co-star Romany Malco. "You have all these unpredictable circumstances [on reality TV], because life is so bizarre. You get to sneak some of that in with improv."

Leslie David Baker, sad-faced Stanley on "The Office," also said people are drawn to the form because it reflects their own lives. "People are realizing that improv is something they do every day at work. There's a bunch of people looking at you, waiting on you to do something, so you have to come up with something off the top of your head. We do the same thing, in many cases, on our show."

Over the last half-decade, pop culture has witnessed a revolution that favors awkward silences instead of traditional "setup, punch line" comedy. To many, it's a sign of the times. But undoubtedly, names like Milton Berle, Don Rickles and Richard Pryor possessed similar quick wits long before the term "improv" was popularized in the '70s.

"The whole 'Tonight Show' was improv," insisted beloved sidekick Ed McMahon, who spent three decades crafting sketches and interviews on the fly alongside Johnny Carson. "We had no script; we just showed up with a clean shirt and did it. Most of the best things that ever happened on that show were unplanned. You've probably seen the scene where the little cougar scares [Carson], and he runs over and jumps in my arms? You couldn't write that; that just happened."

Eddie Murphy said he has relied on improv his whole career. "Improvising has always been a big part of the creative process for me," he said. "I have to be allowed to improvise whenever I'm making a movie. I have to be able to say or try something that's not on the page, so I've always done it. Coming from 'Saturday Night Live,' and coming from stand-up comedy, your act starts out improvising when you get on the stage for the first time. Anybody that started doing stand-up comedy, their roots are improvisation."

(Watch Eddie Murphy riff on improv comedy.)

"Saturday Night Live" co-creator Lorne Michaels agreed. "It's a very good tool for creating comedy," he said. "There was a moment years ago, during the first five years, when Steve Martin was doing a monologue, and Bill Murray was taken from the audience [playing a normal person]. ... Steve said, 'Have you ever been on television before?' And Murray said, 'Once, at a Cubs game, in a long shot.'

"You could only laugh," Michaels recalled, "and go, 'Where'd that come from?' "

(See Lorne Michaels recall Steve Martin and Bill Murray's hilarious exchange.)

But in this new heyday of unscripted laughs, who, exactly, is the quickest comedian in the game?

"The current Babe Ruth of improv?" Rogen pondered. "Sacha Baron Cohen. He's pretty amazing."

"Office" co-star Phyllis Smith had someone else to champion. "I happen to be partial to Steve Carell," she said. "I've watched him take one scene and do it 12 different ways, and be brilliant in every one."

"It's probably Will Ferrell," grinned ... Will Ferrell. "But I don't know. I'm just an objective individual."

But Jon Heder insisted that his "Blades of Glory" co-star isn't just his own biggest fan. "Will just kind of whips them out," Heder said. "He's got a backpack of jokes on him at all times. It's like one of those beer helmets: He puts it on, and he just has a little tube to his brain."

"What about John C. Reilly?" "Balls of Fury" star Dan Fogler said. "You don't consider him to be a great improviser, you consider him to be a great actor. But he's fantastic."

"Amy Poehler is pretty remarkable," said Michaels, calling her the best improv comedian ever to work on "SNL."

Prior to "SNL," Poehler established herself at Chicago's Second City and ImprovOlympic -- it was at the latter place where she helped birth the Upright Citizens Brigade, the lauded underground sketch-comedy troupe that had a short-lived Comedy Central show and has a pair of self-titled comedy theaters in New York and Los Angeles.

"We started with Del Close, the most famous person in improv comedy," Poehler said of the UCB troupe. "He's the person that you should be talking about; he taught every great Chicago improviser and sketch person."

(See Will Ferrell, Will Arnett, Amy Poehler and Jenna Fischer improvise an off-the-cuff routine.)

Close -- whose final words were reportedly, "I'm tired of being the funniest person in the room" -- invented many of the improv techniques five decades ago that still impact today's top comedians.

"He used to say, 'Agree and add. Take what is, and add to it,' " Myers remembered. "He also had a great expression: 'The master weaver takes the mistakes of his students and weaves them into the grand design.' "

"There's a science. You're supposed to say, 'Yes, and ...,' " explained Ben Garant, a founding member of the comedy group the State and star of "Reno 911!" "No matter what anybody says to you -- 'We live in an ice-cream shop!' -- you agree with them and then add something. 'Yes, an ice-cream shop in outer space!'

"But on 'Reno 911!' we say, 'No, shut up, f--- you, we're not in an ice-cream shop, sir,' " Garant added, explaining how they've flipped the formula to create conflict on his cop show. "We kind of ignore what you're supposed to do."

But whether a comedian cites Close or other pioneers like Viola Spolin, Paul Sills or Keith Johnstone as a mentor -- and whether they come from Second City, L.A.'s the Groundlings or so many other theater groups in the country -- they all agree that practice makes perfect.

"Do as much as you possibly can and don't worry about getting paid for it," Carell advised those looking to get into comedy. "Don't be precious about looking for the big break, or that special moment. Just do it; just do it as much as you can. ... "Start with your family; embarrass them in public. That's what I always used to do."

It's that mentality that begins to explain the latest wave of improv masterminds -- people like Rogen, Andy Samberg, Michael Cera and Jonah Hill, who possess far less formal training than the previous generation but are pioneering a sleeker, more natural style. "If you're going to be funny, come here and work," the 24-year-old Hill said of the mindset behind a day on the set of something like "Superbad." "And if you're not, then stay home."

"But the way we improvise is very conversational; we don't expect people to come up with brilliant jokes," Rogen said. "It's mostly just naturalizing the dialogue and saying things how [normal people] would say it.

"[Cera and Hill] are definitely very talented improvisers, but I'm not going to jump to saying they're better than Abbott and Costello," the 25-year-old Rogen said of comparisons between modern-day funnymen and their quick-witted predecessors. "I wish I was on set when they made some of those Laurel and Hardy movies, just to see how much was thought up off-the-cuff."

Harry Shearer, part of the Christopher Guest family, gave a word of caution to fans and would-be improvisers: "There's good improv and there's bad improv, and there always has been and there always will be," he said. "I was a fan of some early improv groups when I was coming up, and I was really amazed with what they did. And I have seen some improv in clubs, and been appalled by it. There's not a magic formula. It depends on the talent of the people involved."

(Watch Harry Shearer explain why the good comes with the bad in improv comedy.)

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