Is it illegal to sell or rent M (Mature) and AO (Adults Only) games to children under 17 and 18 years of age respectively?

While the ESRB does not have the authority to enforce its ratings at the retail level, it does work closely with retailers and game centers to display information that explains to customers how the rating system works. Many major retailers currently have their own store policies requiring age verification for the sale or rental of M (Mature) and AO (Adults Only) rated games, and ESRB encourages and supports these efforts. A mystery shop study conducted by the U.S. Federal Trade Commission (FTC) found that national retailers enforced their store policies by refusing to sell M-rated video games to minors 87% of the time.