Consider this tale of two books: Both set in exclusive prep schools, narrated by teenaged outsiders, featuring sex scenes that would make a tuition-paying parent cringe. Both are first novels, written by 20-something authors, tackling Big Issues—class, race, love, life, death.

One is Prep by Curtis Sittenfeld, published in January by Random House, which has sold 200,000 copies since its release. The other, Looking for Alaska by John Green, published by Dutton Children's Books in March, has also been a hit—but by the more modest standards of young adult publishing—selling 30,000 copies.

Side by side, these books illustrate the increasingly blurry line between titles designated as YA and those put on adult lists. With once-taboo subjects now widely accepted in YA titles and adult authors lining up to pen books aimed at teen readers, deciding which audience to target with any given book is a subjective matter driven as much by personal taste and commercial considerations as by any clear-cut rules about content or quality of the writing. As numerous recent examples show, one publisher's YA book could be another's adult novel. While that may complicate publishing decisions, it also is opening up opportunities for publishers to market their books to a crossover audience.

Though people will reach back as far as The Adventures of Huckleberry Finn and Little Women in search of YA's antecedents, there's widespread agreement that Holden Caulfield is the grandfather of today's angst-ridden, wisecracking, often unreliable teenage narrator. That said, "Young Adult" is a classification created by librarians long after Salinger wrote his classic novel.

Some experts say today's YA books are defined mostly by their tone, and the narrator's perspective. A wistful, wiser-now voice of an adult looking back at his youth is the surest way to get a book booted from YA to adult, says editor and author Marc Aronson, a YA specialist. "It's not just how much sex or how much violence but ultimately what distance is there between the narrator and the experience she's going through," Aronson said. "If the narrator is immediately in the experience, it's YA. If they're telling the story at some remove, it's not."

Shana Kelly, the William Morris agent who submitted Prep to 14 publishers before Random House accepted it, agrees. "A few of the editors who passed on the manuscript specifically said they thought it should be published as YA, but I didn't agree. The narrator is looking back at her teen years from a more mature perspective," Kelly says.

But one could hardly accuse Christopher Boone, the narrator of Mark Haddon's The Curious Incident of the Dog in the Night-Time, of telling his story at a remove. The book is one of the most successful crossover titles in years, and Haddon pushed for it to be published for adults, to differentiate it from his backlist titles aimed at a younger readership. In Great Britain, the book was simultaneously published in two editions with different covers, one for adults and one for teenagers, with both editions becoming bestsellers and winning a fistful of awards.

Despite that success, the book's U.S. paperback publisher, Vintage Books, decided not to publish a YA edition, fearing it would be the "kiss of death" for adult sales. "The minute you say something is for kids, it's a turn off," says editor-in-chief Marty Asher. Still, concerns about a YA taint harming adult sales won't stop Asher from publishing a paperback edition of The Burn Journalsfor the adult market. Brent Runyon's memoir of having set himself on fire at age 14 was released in hardcover by Knopf's children's imprint last fall and has sold 25,000 copies. "To some extent, it's an 'eye of the beholder,' thing," Asher says, "But I read about 50 pages and thought, 'This is not for kids. We could get a much larger audience.' "

Sex and the Young Reader

Not so long ago, it was easy to decide a book should be published for adults. Sex, drugs and alcohol abuse were all considered too mature for young teen readers. Judy Blume's Forever (1975) would surely be released as a YA today. "It was a surprise, shock, to me when I read that Forever was my first adult novel—since I never intended it be," Blume says. Her editor Dick Jackson created a special line of adult books at Bradbury Press, into which he published Forever, which dealt with a teen's first sexual experience.

"They were all adult books in the same way that we thought A Separate Peace was an adult book," he said. "It wasn't really, but it wasn't really a children's book either, as defined at the time." He said the intent was to buffer both Blume and the fledgling Bradbury from the backlash he anticipated. "We were trying to sidestep the tut-tutting of the world," Jackson says.

Compare that to today, when Penguin's Razorbill imprint, which targets older teen readers, has published Teach Me, R.A. Nelson's debut book, which chronicles an emotionally devastating affair between a high school student and her teacher. Nelson's agent, Rosemary Stimola, says that just a few years ago she might not have thought of the book as a YA title. "I probably would've pitched it as adult first," Stimola says.

YA's boundaries had to expand for the books to remain relevant, says Mark McVeigh, a senior editor at Dutton. "The lives of kids today are barely recognizable from the childhoods anybody over 30 led in the way they approach sex, drugs, alcohol, parental attention or the lack thereof," he said. McVeigh sought out James St. James, author of the adult nonfiction title Party Monster (Simon & Schuster) and signed up Freak Show (spring '07) a YA novel about a Florida teen drag queen. "It certainly could find a place on an adult list, but James wanted to write a book for kids," McVeigh says.

St. James is not alone. A long list of writers established in adult fiction—Walter Mosley, Joyce Carol Oates, James Patterson, Ridley Pearson, Alice Hoffman, Francine Prose—have published novels with juvenile imprints this year. This despite the fact that advances are typically much lower for YA books and, until very recently, only Harry Potter dared to charge adult money ($29.99) for a kid's book.

"The cynical view is that their agents are saying, 'Hey, there's a huge market out there. Let's sell some books,' " Aronson says. "It's just a retail play at some level—they don't even need reviews. The chains will take those books just based on who the author is." But he suspects there's more at work than that: "Being paid less also means less pressure."

Prose, whose first YA title After (HarperCollins) chronicled life in a high school resembling a police state, agrees. She says she found writing for a younger audience liberating. "I could use a kind of more direct, though not at all dumbed-down, narrative technique, cliffhanger endings at the conclusion of chapters, etc.," Prose says. "And I loved writing in the voice of a 15-year-old boy, it just came pouring out."

So if crossovers are hot, do they cross both ways? Conventional wisdom—as seemingly confirmed by the sales figures for Prep and Alaska—is that kids will reach up to read books designated as adult, but it's tougher to get grown-ups to reach down. There are signs, though, that indicate adults aren't necessarily put off by a YA label. Meg Rosoff, an American living in London, published her first novel, the Printz Award—winning How I Live Now, as a YA title in the U.S. and Great Britain "mainly because the field is a little more open than for adult books," she says. "However, Penguin UK pretty much immediately decided to go for the 'golden egg' which is a crossover book, and I was given two publicists (adult and YA) and two sales teams." The strategy worked. The paperback edition alone has sold 100,000 copies in the six weeks since its July release.

The U.S. paperback release for How I Live Now is scheduled for summer 2006. Chip Gibson, president and publisher of Random House Children's Books, says he's hoping the book will crossover into an adult readership. "The fact that it is published by Random House Children's Books does not limit the audience for whom the book is intended."

Corbett reviews children's books for the Miami Herald and is the author of 12 Again (Dutton).