Chris Vognar

Jason Reitman is a hot young director, but he's also a student of comedy. So when it's time to discuss his new film, the sublimely smart Juno, he's quick to quote one of the all-time greats.

"Billy Wilder used to say, 'Great screenplay, great actors and the rest will figure out itself,' " he muses during a recent stop in Dallas. "That's the situation I found myself in here."

Here's something Wilder didn't say, but might as well have: Smart people find other smart people to work with.

For Juno – the teen pregnancy comedy that conjures a perfect tone of sweetness, edge and emotional truth – he scored the debut screenplay from white-hot scribe Diablo Cody, a former stripper blessed with one of the most original writing voices to come along in years.

Then, for the title role, a 16-year-old bundle of cynicism, naiveté and expectancy. Mr. Reitman cast little-known Canadian actress Ellen Page (nominated Thursday for a Golden Globe for the role) and surrounded her with top-notch character actors, including Allison Janney, Jason Bateman, Michael Cera and J.K. Simmons. The closest thing to a star is Jennifer Garner, and she does the best work of her career.

Fox Searchlight

A couple (Jennifer Garner and Jason Bateman) wants to adopt a pregnant teen's (Ellen Page) baby in Juno.

Great screenplay. Great actors.

Great movie.

None of which is to say Mr. Reitman just sat back and cashed his paycheck. The son of '80s comedy king Ivan Reitman (Stripes, Ghostbusters), he shows the same deft touch here that made his feature debut, 2005's Thank You for Smoking, such a toxic joy. He is, after all, the man in charge.

And even at the age of 30, he was wise enough to know he scored when a friend sent him the Juno screenplay.

"I read it and I wasn't even halfway done when I realized it was just perfect," he says. "I like material that takes a subject matter normally considered untouchable or tricky and deals with it in a very frank or humorous manner. She does all of these little change-ups. You feel like you know who these characters are, but they keep changing on you into something different than what you thought."

Ms. Page was just as big a find. Like Mr. Reitman (and Mr. Cera), she's a Canadian. She's probably best know for her role in the last X-Men movie, but she was remarkable in An American Crime, a powerhouse indie that premiered at Sundance in January but hasn't seen the light of day because its storyline, based on a real-life torture incident in the American heartland, is a bit hot to handle.

"Juno is a character written with this slightly heightened dialogue, and we needed an actor who would come at it with complete realism," Mr. Reitman says. "What I like about Ellen is that no matter what she's doing, she brings honesty. She never plays something up or has a movie moment or plays something as a joke. Her way in is to find the most authentic path to do the character."

Mr. Reitman has his own screenplay in the works, which he's not yet ready to discuss. He'll be more of an authorial presence before too long.

For now, he's happy to get by with a little help from his talented friends.