Producer Mason Novick originally approached Diablo Cody to adapt her stripper memoir 'Candy Girl' for film, but suggested she first write a spec screenplay to showcase her writing to studios; that sample became Juno.

Diablo Cody wrote the screenplay in just seven weeks at the Starbucks inside a Target store in Crystal, Minnesota, and drew heavily on her own high school experiences, including a boyfriend who loved tic-tacs (the basis for Paulie) and a hamburger phone identical to her own.

The script was turned down by several major studios due to its controversial subject matter before John Malkovich's production company Mr. Mudd took it on, and it was later brought to Mandate Pictures.

Jason Reitman had no feature directing credits yet when he pursued Juno, since his first film Thank You for Smoking had not been released; he still fought to direct it, feeling he would regret it forever if he didn't.

Reitman decided to cast Elliot Page as Juno after admiring his performance in Hard Candy, and pictured Page in the role from his first read of the script; he traveled to Page's film set to personally offer him the part.

Reitman gave the script to J.K. Simmons without telling him which role he intended for him; Simmons said he would have happily played even the silent high school teacher role.

To present a cast package to Fox Searchlight, Reitman filmed a 45-page screen test on 35mm film with Page, Simmons, Olivia Thirlby and Michael Cera against a black backdrop at a Panavision stage, believing screen tests together were essential since the film was about relationships.

Jennifer Garner accepted a lower salary than usual to help keep the film within its $6.5 million budget, and she recommended Jason Bateman for the role of Mark after working with him on The Kingdom; Bateman was the last actor cast.

DJ and record producer Cut Chemist (Lucas McFadden), who was doing scoring work for Reitman, makes a cameo as the chemistry teacher — a casting choice Reitman called 'perfect irony'.

Although Vancouver often substitutes for American locations for budget reasons, Reitman insisted the choice to shoot there was made specifically at his request, standing in for Minnesota.

Filming took place over just 30 days in February and March 2007; unexpected real snowfall allowed the crew to shoot winter scenes with actual snow instead of importing fake snow, resulting in wider snow shots than planned.

The final scene, set in summer, was scheduled for the last day of shooting; after a long stretch of rain threatened to postpone it for months, the weather cleared just in time to shoot it in the sun.

To depict changing seasons despite the short 30-day shoot, the crew used fake flora, including composited brown leaves on a tree, lighter-pink touched-up cherry blossoms for autumn, a fan to blow artificial falling leaves, and fake flowers for the summer ending.

Elliot Page wore two sizes of prosthetic pregnancy bellies fitted like a corset, plus a third 'real' belly used for the ultrasound scene, along with various sizes of fake breasts.

The footage shown on the ultrasound monitor in Juno's scene was actual footage of supervising sound designer Scott Sanders's own son, embedded digitally in post-production.

Elliot Page suggested using The Moldy Peaches' music to Reitman, playing songs for him on his computer, which led Reitman to contact Kimya Dawson, who sent a packet of about 120 self-recorded songs for consideration.

Composer Mateo Messina created the film's instrumental score using a worn, out-of-tune secondhand guitar nicknamed 'Stella,' played by guitarist Billy Katz, to match the loose acoustic feel of Kimya Dawson's music.

Reitman found the opening-titles song 'All I Want Is You' by Barry Louis Polisar after hours of searching iTunes, and built the entire opening title sequence around its handmade, innocent quality.

For the rotoscoped opening title sequence, Elliot Page was filmed walking on a treadmill drinking SunnyD; 900 resulting still images were repeatedly run through a Xerox machine to degrade them until they looked hand-drawn, then composited into an animated sequence.

Following the film's release, Fox Searchlight sent hamburger phones like the one used by Juno to journalists and critics as promotion; unaffiliated companies then began selling similar phones online, with eBay sales increasing 759 percent in the month after release.

Juno earned back its entire $6.5 million budget within twenty days of release, nineteen of which were during its limited theatrical run, and went on to gross over $232 million worldwide, becoming Fox Searchlight's first film to surpass $100 million.

After 17 students under 16 became pregnant at a Massachusetts high school in 2008, Time magazine coined the term 'Juno Effect,' with some commentators accusing the film of glamorizing teen pregnancy.

Reitman was frustrated that Juno was ruled ineligible for Canada's Genie Awards despite its Canadian director, cast, and crew, because its sole financiers were the American companies Mandate Pictures and Fox Searchlight.