NC-17 films are a classification given by the Motion Picture Association (MPA) to movies that contain content deemed inappropriate for viewers under 17 years old. This rating often indicates explicit sexual content, but it can also include extreme violence or other adult themes. Unlike the R rating, which allows viewers under 17 to attend with an adult, NC-17 films are not suitable for anyone under 17, effectively limiting their audience. The NC-17 rating was introduced in 1990 to replace the previous X rating, which had become associated with pornography. While some filmmakers aim for this rating to signify artistic expression, many studios avoid it due to the stigma and potential box office limitations. As a result, NC-17 films are relatively rare in mainstream cinema.