The Motion Picture Association of America initially adopted the film-rating
system that ranged for "G" to "X." In 1984 the PG-13 (Parental Guidance
under age 13) was added and X was changed to NC-17 around 1990. The
movies are rated by a specially selected committee of the Classification
and Rating Administration after reviewing content for language, sex,
nudity, and violence.

Jack Valenti (above) helped devise the movie-rating system while
he was president of the Motion Picture Association of America from
1966 to 2004.