The movie ratings system was created 36 years ago this month. Eight to 11 citizens are chosen to be on the ratings board. They watch each movie and then vote on what they think the rating should be. They don't all have to agree: Whichever rating gets the most votes is selected.
If the maker of the film disagrees with that rating, the decision can be appealed to -- or reviewed by -- the appeals board. That group is made up of people who make, distribute and show films.
The current ratings came into being in 1984. Before that, movies were rated G for all audiences, M for Mature (all ages could be admitted, but parents were supposed to watch out for younger children), R for Restricted to people over 16 unless they were with a parent, and X for no one under 17 admitted.
Later, the M category was changed to PG -- many people seemed to think that M meant the movies were for viewers older than the ratings board intended. After "Indiana Jones and the Temple of Doom" was released in 1984 with a PG rating, the Motion Picture Association of America, led by Jack Valenti, decided there needed to be a rating between PG and R, and added PG-13. Valenti says it was a scene showing a live, beating heart from "Indiana Jones" that caused them to add the new category.
In the same year, "Gremlins" got a PG rating, but most parents and movie critics felt it was way too scary for kids to see.
In 1990, the Ratings Board began adding descriptions to the letters to explain why movies were rated as they were.