Young-adult fiction or young adult literature (often abbreviated as YA), also juvenile fiction, is fiction written, published, or marketed to adolescents and young adults, although recent studies show that 55% of young-adult fiction is purchased by readers over 18 years of age. The Young Adult Library Services Association (YALSA) of the American Library Association (ALA) defines a young adult as someone between the ages of twelve and eighteen. Authors and readers of young adult (YA) novels often define the genre as literature as traditionally written for ages ranging from sixteen years up to the age of twenty-five, while Teen Fiction is written for the ages of ten and to fifteen. The terms young-adult novel, juvenile novel, young-adult book, etc. refer to the works in the YA category.

YA literature shares the following fundamental elements of the fiction genre: character, plot, setting, theme, and style. However, theme and style are often subordinated to the more tangible elements of plot, setting, and character, which appeal more readily to younger readers. The vast majority of YA stories portray an adolescent, rather than an adult or child, as the protagonist.

The subject matter and story lines of YA literature are typically consistent with the age and experience of the main character, but, beyond that, YA stories span the spectrum of fiction genres. Themes in YA stories often focus on the challenges of youth, sometimes referred to as problem novels or coming-of-age novels. Writing styles of YA stories range widely, from the richness of literary style to the clarity and speed of the unobtrusive and free verse.