The first movie trailers occurred at the end of the films. They were called “trailers” because the advertisements would be spliced directly on the end of the reels, so that the movie advertisement’s film trailed the actual film.
The first known movie trailer to appear in a theater was in November
of 1913. It was made by Nils Granlund, advertising manager of Marcus
Loew theaters in the United States. The trailer was for the musical
The Pleasure Seekers, which was shortly to open on Broadway. In this
trailer, he included short clips of rehearsals of the musical. This
idea caught on and trailers began appearing routinely after films.
This was particularly the case with cartoon shorts and serials that
would often end in climactic situations where you needed to watch
the next episode in the serial or cartoon to see what would happen.
Thus, these trailers, in particular those that advertised the next
episode, made a lot more sense at the end of the serial than at the
Movie studios realized that full film advertisements would be more
effective if they showed up before the movie, instead of after, and
by the end of the 1930s the switch had been made. Despite the
industry’s sincerest attempts over the last 60 or 70 years to get
the name changed from “trailers” to some form of “previews”, among
industry professionals and English speaking audiences “trailer” is
still the generally used term. Recently the general public has begun
to use 'previews'.
Of the ten billion videos watched online, movie trailers rank third,
after news and user created videos.