X - MPAA Movie Rating for Adults Only by

The Best X-Rated and NC-17-Rated Movies in History

History

X-Rated: The Greatest Adult Movies of All-Time (2015) - DVD PLANET STORE

Mpaa rating review by Horseboy223 on DeviantArt

Dirty movies: A Top X List - DenOfCinema

Adult rating, Rating System Wiki

The NC-17 Rating Needs To Go

X (MPAA), Rating System Wiki

A 'No Children' Category To Replace the 'X' Rating - The New York Times