Any moviegoer 17 or older can see an R-rated movie. At the movie theater, you will be asked to show your ID attesting to your age. This ID should be a state or federal government issued ID such as a passport or license, but most movie theaters will accept a valid high school or college ID that clearly states your birthdate.
Children under 17 years old can see an R-rated movie when accompanied by an adult guardian or parent. The age of an "adult guardian" varies by jurisdiction, and may be 18 or 21. Patrons should call ahead to the theater where they would like to see the movie to verify what age constitutes an adult guardian.
In 2004, GKC theaters began offering the controversial "R-cards." The purpose of these cards was to allow teens and children under 16 to see R-rated movies with an accompanying adult guardian or parent. These children must apply for the R-card with a parent present, and the theater recommends that the parent hold on to the card and only give it to the child to see certain movies. The theater's motivation for creating these cards was that certain R-rated movies were rated too harshly by the MPAA, in their opinion, and children were being shut out of movies that were not harmful to them.
A movie that has earned an NC-17 rating should not be confused with an R-rated movie. These films are not open to anyone 17 and under. That means you have to be 18 to see the movie, and it does not matter if you are accompanied by a parent or adult guardian.