On the topic of ‘crossover literature’, Regina Brooks explains:
“A lot of people in the publishing industry believe that confusion about what constitutes YA it is heightened by the success of some titles known in the industry as “crossovers.” Publishing houses generate additional revenue from some books by marketing them to both adult and YA readers, thus crossing over from one audience to another. Francesca Lia Block’s cult novel, Weetzie Bat, written in 1989, is considered the original crossover, continuing to attract readers from fifteen to thirty-five. Two of the most commercially successful crossovers are Mark Haddon’s The Curious Incident of the Dog in the Night-Time and Yann Martel’s Life of Pi. Both were published in 2002 and have sold over two million copies each. Those books were adult books that crossed over into the YA market, but there are others that start out as YA and then cross over to an adult audience; for example, Stephanie Meyer’s Twilight series and Cecily von Ziegesar’s Gossip Girl series. The first became a feature film and the second a popular television series.
Author of the crossover series Harry Potter, J.K. Rowling has said she had no particular age group in mind when she started writing Harry Potter and the Sorcerer’s Stone; however, she did know she was writing for children. The first Harry Potter novel was eventually published in 1998 by Scholastic, the world’s largest publisher and distributor of [-p.xiii] juvenile books. The company targeted Harry Potter to children nine to eleven. What happened, of course, made publishing history, with Rowling’s work garnering millions of fans worldwide, both older and younger, including a substantial segment of teens. Later, two separate editions of Harry Potter were released, identical in text but with the cover artwork on one edition aimed at children and the other at adults.
Rowling’s young wizard also cast magic on the YA world, changing the way the industry viewed the genre. Harry Potter‘s $29.99 selling price reminded publishers that young people were not only willing to shell out big bucks to read but that they also had the means to do so. In 2006 in the United States alone, teens had $94.7 billion a year to spend, a figure that increases about $1 billion a year, according to Jupiter Research.” (pp.xii-xiii)
Ref: Regina Brooks (2009) Writing Great Books for Young Adults. Sourcebooks, Inc.: Naperville, Illinois