Will Gluck, a director and screenwriter whose credits include Easy A, Friends With Benefits and several TV series, had never written a musical prior to getting the job of updating the classic Broadway hit Annie. He hired two songwriters who also had no experience in musicals: Sia Furler (of "Chandelier" fame) and Greg Kurstin.

'Annie' Director Will Gluck Worried He'd 'Ruin a Lot of Kids' Childhoods'

"I met with a lot of songwriters and I immediately fell in love with Sia," says Gluck, 42, who also provided input on casting, music and editing for the Columbia Pictures film that opens Dec. 19. "She introduced me to Greg, who had to learn quickly. I'd say, 'We need a piece of score here,' and he'd say, 'What does that mean?' "

Final 'Annie' Trailer Has Sia's 'You're Never Fully Dressed Without a Smile'

To ease Furler and Kurstin into the process -- they started work on the film in March 2013 -- Gluck would give a songs's title, its intended goal, where it fit in the script and who would perform it (the film stars Quvenzhane Wallis). Kurstin then created a sonic palette for the entire film, giving the classics "It's the Hard Knock Life," "Tomorrow" and "You're Never Fully Dressed Without a Smile" the same feel as new tunes "Opportunity," "The City's Yours" and "Who Am I."

Watch Gluck and Kurstin talk about the music for Annie at the recent Billboard & THR Film & TV Conference: 

"We had a lot of discussions before we started, especially about the songs we reimagined," says Gluck. "For 'Little Girls,' we took Martin Charnin and Charles Strouse's basic melody and made it our own. What Greg and Sia did was so expert: giving a nod to an old song that, if you've never heard it before, stands on its own. ... The only way it works is if [the song] has strong bones to begin with. It's very strong-boned music."

This article first appeared in the Nov. 15 issue of Billboard.