"The trailer is the single most important piece of advertising about a movie," said CBS Films co-president Terry Press. "There's nothing else that comes close. And if you have a bad one, and people go apeshit on the Internet and don't like it, some filmmakers never recover." (Indeed, the trailer is important enough to the movie-going public that The New York Times published an interactive feature last year devoted to dissecting the trailers of new films compared with the chronology of the movies themselves—and more recently, Wired produced an entire series celebrating and analyzing our national obsession with coming attractions.)

It may seem like the Internet age has upended some long-standing traditional formula for trailers the way it has upended long-standing traditions in virtually every other form of art and entertainment. But a look back into the history of the movie trailer shows that film previews have almost always been in the process of evolving, almost always directly influenced by the pop-cultural landscapes that created them.

Coming attractions have been part of the movie-going experience for a century now. (In the early days, movie houses ran trailers after a film's conclusion rather than before a film began—they were called "trailers" because they trailed the feature film.) In the blockbuster-rich 1940s, film trailers were built around how you might sell a moving picture to a stage-going audience, or to someone listening on the radio. It was the era of "the hypersell," according to Press: "If you look at the ones in the ‘40s, there were so many movies and so many people going to movies, they were all sort of over-the-top with the copy, like, 'This is the greatest movie of the year!' They used big, giant claim-lines."

For instance, check out the trailer for 1940’s The Philadelphia Story:

The time between cuts, and the overall pacing, drags by today's standards. It runs nearly four minutes long. The tone is completely over-the-top, promising a "star-packed, laugh-laden, romantic smash." The trailer opens and closes with the title card and actors' names in lights—again, an image that evokes the stage more than the silver screen. (This makes sense, on one level: The Philadelphia Story was written as a play and proved a hit on Broadway, also starring Katharine Hepburn, before it was adapted to film.)

In the 1950s, as television came into its own, the narrative devices in film trailers mirrored what people were seeing on TV and in print, the influential media of the day. In the trailer for 1954’s Rear Window, the narrator sounds as though he could be selling toothpaste in the typical, polished-but-hyperbolic tone you'd hear in TV spots of the era. At one point (around the 1:40 mark), lead actor Jimmy Stewart breaks character to turn and address the audience about the film, looking directly into the camera—a narrative style that was a hallmark of 1950s-launched programs like Alfred Hitchcock Presents and The Twilight Zone.

The trailer concludes with two frames that look like print ads; they're text-heavy and voiceover-free, left for the audience to read: "SEE IT! If your nerves can stand it after Psycho. And see it from the beginning of course."