The Entertainment Software Rating Board (ESRB) is an organization that rates video games. Rating is voluntary. Game publishers do not have to submit their games for ratings. There are seven ratings: E (Everyone), E10+ (Everyone 10+), T (Teen), M (Mature 17+), AO (Adults Only), and RP (Rating Pending). Some retailers make people show identification to prove their age if they want to buy M-rated games. Many retailers will not buy and sell AO games so it is very hard for gamers to find AO-rated games.