Young adult fiction (YA) is fiction written for readers from 12 to 18 years of age. The term YA was first used regularly in the 1960s in the United States. The YA category includes most of the genres found in adult fiction, with themes that include friendship, sexuality, drugs and alcohol, and sexual and gender identity. Stories that focus on the challenges of youth may be categorized as problem novels or coming-of-age novels. The boundary between children's and adult literature is flexible, subject to moral and political ideology, and in some cases meaningless. The designation of young adult fiction was originally developed by librarians to help teenagers make the transition between children's and adult literature, following the recognition, around World War II, of teenagers as a distinct group of young people. While the genre is targeted at adolescents, a 2012 study found that 55% of YA readers were adults. Source: Wikipedia (en)