 The MPA rating system is a voluntary scheme that is not enforced by law; films can be exhibited without a rating, although certain theaters refuse to exhibit non-rated or NC-17 rated films.Non-members of MPA may also submit films for rating.<ref></ref> Other media, such as television programs, music and video games, are rated by other entities such as the TV Parental Guidelines, the RIAA and the ESRB, respectively.Introduced in 1968,<ref name=desques></ref> the MPA rating system is one of various motion picture rating systems that are used to help parents decide what films are appropriate for their children.