Lauren Oliver may have just published Before I Fall (Harper), but she's been writing for as long as she can remember—"every day since I was about five," she says. "I've had dozens of books in various stages of completion, and I wrote two full adult novels, one of which had absolutely no plot. It was in the YA world where I learned about narrative tension."

Oliver's entry into YA publishing wasn't deliberate, though—not at first. "I was working on adult stuff at NYU, where I was getting my M.F.A. in creative writing," she says. "But then I started working as an editorial assistant at Razorbill, and suddenly I was reading six to eight YA novels a week. That's when I thought of Sam."

In Before I Fall, Sam is a 17-year-old girl caught in a time loop, dying at the end of each day only to wake up and relive the same day again. To Oliver, the device of the repetition is secondary to Sam's character.

"I wanted to write about a girl who was selfish and disconnected from what is meaningful in her life—a character study," Oliver says. "I wrote the prologue and the epilogue first, and Sam's emotional, internal responses are very different in those two passages. Then I thought hard about what set of circumstances would allow her to experience that amount of change and growth in a very short amount of time, which ended up being through the mechanism of Sam reliving her last day many times over."

Oliver identifies a lot with Sam on a personal level, too. "I was definitely nicer than Sam in high school but not much, unfortunately," she says. "I acted out and a lot of my behavior and meanness was about feeling lost, so I wrote about that through Sam. But I connect to all of my characters in some way: to Lindsay, who hides her insecurity behind viciousness, and even Juliet, who feels she's too broken to re-enter the world." But, she adds, "I'm a lot nicer now!"

Oliver describes the road to acquisition for Before I Fall as "rather fairy tale-esque."

"I met my agent, Stephen Barbara, back when I was an undergraduate at the University of Chicago—we were both students. He knew me as the girl he saw walking across campus with high heels always yapping into her cellphone," she says with a laugh. "When I told him about my manuscript, he agreed to meet, and honestly, he was the only agent I submitted to. I appreciated his vision and drive and knew he'd be an incredible advocate for my book. And he was—we had a pre-empt from Harper within three days."

While the acquisition process was smooth, Oliver did experience some bumps before publication. Though her book was originally acquired by Brenda Bowen, Bowen left Harper shortly afterward, so for a while Oliver's book was "orphaned." But then Before I Fall landed with Rosemary Brosnan, executive editor at HarperCollins, and she and Oliver clicked right away. "Rosemary is an incredible, meticulous editor—she pores over every word and cares deeply about language, which I love. And I can't believe how supportive everyone at Harper has been throughout."

Most unexpected is Oliver's sudden aversion to entering bookstores since her novel's publication. "I thought I'd rush to bookstores, but now I avoid the YA sections because it makes me nervous," she says. "The other day I actually saw a girl pick up my book, and I went up to her and told her that I wrote it, because I have no capacity to censor myself," she says, laughing.

Oliver writes every morning—on the subway (she lives in Brooklyn). "Writing is one of the few things you can do when you are underground," she explains. But she divides her day between working on her own novels and developing book ideas for the company she recently started, Paper Lantern Lit, with former Razorbill colleague Lexa Hillyer.

As for what's next, Oliver's fans not only don't have long to wait but will be happy to know that it's the first book in a trilogy. Called Delirium, it comes out next February from Harper.