Film deterioration is no laughing matter.

Earlier this week, the Library of Congress' National Film Registry announced this year's selection of 25 films, a list that includes The Exorcist, All the President's Men, The Empire Strikes Back, Airplane!, Malcolm X, and Saturday Night Fever. To quote the press release, "These films are not selected as the 'best' American films of all time, but rather as works of enduring significance to American culture." There's no point, then, in getting upset that The Pink Panther has joined the registry while Hud remains in waiting. But what does being selected mean, exactly, for these movies?

Preservation, first and foremost. NFR coordinator Steve Leggett says the registry's first task is to determine if these 25 films have been preserved by a movie studio, film archive, or the Academy of Motion Picture Arts and Sciences, "and if it hasn't, we'll work with them to make sure they preserve it." That help may come in the form of financial assistance, or by having the film sent to the Library of Congress for preservation. As for what preservation entails, it depends on the film's state. Consider two new additions: Study of a River, an experimental film from 1996, is likely in fine shape, but 1891's Newark Athlete could probably use a restoration. Prior to 1950, movies were made on highly flammable nitrate film, and thus are in need of conversion to safety film. Color movies made before 1980, meanwhile, need to be copied to fade-resistant stock.

Regardless of the movie's year, the registry ensures that film and digital copies are made, if they don't exist already. This is not cheap — a recent restoration of Fritz Lang's Metropolis cost $840,000 — so it's probably a good thing that not all of the films added to the registry are desperately in need of preservation. A 35mm print of every film is added to the library's collection, though they're only available to "researchers who are doing something that will be publicly available," says Leggett. ("I think you can get most of these titles on DVD or YouTube," he adds.) And if the film was made before 1920, and thus part of the public domain, then library makes it available online.

I asked Leggett if, in coming decades, films shot in digital would be added to the registry. "Right now, technically, they wouldn't be eligible because they wouldn't be on film stock," he said, but noted that the legislation establishing the NFR could always be changed. Surprisingly, digital films will need preserving, too: Leggett says that digital files can deteriorate in as few as five years, while properly preserved films — 32 degrees Fahrenheit, low humidity — "will last hundreds of years." On New Year's Eve, I plan to impress all sorts of strangers with this counterintuitive fact.

Oh, and I also asked Leggett to name his favorite 2010 addition to the registry: 1934's It's a Gift, starring W.C. Fields. Mine would have to be 1906's A Trip Down Market Street. Obviously.