A motion picture rating system categorizes films with regard to suitability for audiences in terms of issues (在…方面) such as sex, violence, substance abuse (酗酒吸毒等不良现象), profanity (渎神) or other types of mature content. In the United States, the Motion Picture Association of America (MPAA美国电影协会), through the Classification and Rating Administration (CARA电影评级机构) issues ratings for movies. The system was instituted（创立） in November 1968 and is voluntary (自愿的); however, most movie theater chains will not show unrated domestic films and most major studios (制片厂) have agreed to submit all titles for rating prior to theatrical release (在影片公映之前).

The ratings as they exist now are:

G — General Audiences — All ages admitted. There is no content that would be 

     objectionable(会引起反对的) to most parents. 

PG — Parental Guidance Suggested — Some material may not be suitable for    

    children. 

PG-13—Parents Strongly Cautioned—Some material may be inappropriate for children under 13.

R — Restricted — Under 17 requires accompanying parent or adult 21 or older. The parent / guardian is required to stay with the child under 17 through the entire movie.

NC-17 — No one 17 and under is admitted.