It was originally called The Big Heart. Daryl Zanuck the shrewd head of Twentieth Century Fox couldn't buy the image of Santa Claus in a court room. But like so many ventures Miracle On 34th Street (1947) came about because of passion, in this case that of Director George Seaton who had gone to New York on his own and made arrangements with the real Mr. Macy and Mr. Gimbel to film inside their department stores. Impressed by Seaton's commitment Zanuck gave the show a green light.

Who would play the little girl who didn't believe in Santa Claus? Seaton agonized over it, until the assistant director remembered an amazing child prodigy from Santa Rosa, California who could cry on cue. Her name was Natasha Nikolaevna Gurdin renamed Natalie Wood after director Sam Wood . The same Natalie Wood who would later go out on a hotel room ledge and threaten to jump when her boyfriend Elvis Presley ignored her to play poker with Memphis Mafia. The same girl who would infuriate fellow cast members of West Side Story (1961) with her tardiness, her refusal to learn simple dance steps and her insistence on long lunch breaks to visit with her analyst. But the seven-year-old Natalie had none of the typical child star precocious behavior, she gained the respect of her co-stars on the Miracle set with her professional demeanor, earning the nickname One-Take-Natalie.

Like all filmed on location movies there were logistical problems. The sequence where Santa was taken to Bellevue was done without permission. The famous hospital would not cooperate with Hollywood because they had been portrayed badly in earlier films, they were not swayed by the sight of a sickly, freezing cold Santa Claus (Edmund Gwenn) bundled up under blankets in a car, waiting to shoot his scenes. The filmmakers were forced to shoot only the car approaching the building's entrance and edit the rest later. Another difficulty was getting permission to shoot the Macy's parade from the apartment dwellers on 34th street which had to be done right the first time, there could be no retakes. The film crew paid the ladies of the house to place the cameras in their windows. Then their husbands came home, complained about the inconvenience and demanded their own equal share. Most difficult to film was the sickly but determined Edmund Gwenn who would win an Oscar for playing Kris Kringle. He suffered from a bladder control problem but couldn't stand the thought of someone taking his place in the parade. The children who stood on the sidewalk waving at Santa never saw the long tube under his cloak.

Overcoming his initial reluctance Daryl Zanuck who was famous for his memos, made suggestions to improve the film's story. The mother Doris, played by Maureen O'Hara was too cold, she would scare a man like Fred (John Payne) off, she had to be made warmer to the audience by explaining that she had been burned by an earlier relationship and that's why she didn't want her daughter believing in Santa Claus. Zanuck also felt that they shouldn't overdo the scenes where Macy's employees recommend that their customers go shopping at Gimbels, just some simple dialogue was enough to get the point across. But despite the loud cheering by preview audiences when Santa Claus was declared sane in the courtroom scene, Zanuck never had full confidence in the film. He put it in theaters in July, the busiest time of year for moviegoers, and told his marketing staff to hide from the public that the film was about Christmas.

One reference in the Miracle script that's now dated was when Kris Kringle's psychiatrist mentioned a man in Hollywood who passed himself off as Russian Prince and owned a restaurant. It was a dig at Mike Romanoff, a colorful fraud whose Rodeo Drive eatery was a fun sanctuary for Hollywood's most notorious figures. One night FBI head J. Edgar Hoover was dining at Romanoffs when he was approached by an actual jewel thief named Swifty Morgan. "Like to buy these gold cuff links?" Amused, Hoover offered $200. "Oh come on John the reward is more than that!"