All Grown Up, Jami Attenberg’s wry tour-de-force of a novel tells the story of Andrea Bern: single, pushing 40, child-free by choice, and doing just fine, she’s living without the reassuring milestones that define “adulthood.” Andrea isn’t married or engaged. She doesn’t have a baby; more radical still, she doesn’t want one.

It is a novel Attenberg spent nearly a year trying very hard not to write.

“I was casting about for what I was going to write next,” she says, when she started in on the story cycle about the shifting friendship between two women, Andrea and Indigo, navigating whatever we’ve amorphously defined as “adulthood." And that was going to be that. “I was like, I don’t want to write this anymore. I don’t feel like talking about what it means to be a grown up,” she says. “I didn’t have any more to say on the matter.” But Andrea’s voice kept following her: she started in on another book, a ghost story, but with the same characters. She shelved that and picked up third project: still Andrea.

“I didn’t want to deal with it,” she tells me from her home in New Orleans. “I had no interest in writing a book about being a single person. At all.” Also, the novel, or what would become it, deals with the meaning of “adulthood,” and frankly, Attenberg wasn’t sure she was all that interested in the question. “If I’m honest, looking at it in retrospect, I didn’t know if I wanted to put myself through the paces of trying to figure out what those answers were.”

And then it clicked. “I said, Alright. I’m just going to sit down and see what comes out and if I have anything more to say on the matter,” she says. “And then I wrote 90 pages in three weeks. It was just all sitting there.”

The book, which is spare and elegant and bitingly funny, circles through time, the vignettes moving forward, then doubling back: with men and with her mother, dropping out of art school, and coping, poorly, with the reality of her brother’s terminally ill child. “I wanted to show you all of her parts,” Attenberg says. “Not just the way society viewed her, but the way she viewed herself.”

It’s a question the novel confronts with startling clarity. “Why is being single the only thing people think of when they think of me?” Andrea asks her therapist, in the book’s anchoring scene. “I’m other things, too.” For example, a woman. A designer. A daughter. A sister. Technically a Jew. “The captain of the sinking ship that is my flesh,” is what she thinks, but does not say.

But if the story is Andrea’s, the quest is universal. “Every character in the book goes through their own specific struggle to claim adulthood,” she says, and the problem is that “adulthood” is an irritatingly unstable category: careers change; marriages end; babies get sick. “I went through this period when I was writing the book where every single conversation I’d have at every dinner party, I was like, ‘What do you think it means to be a grownup?’ ” Attenberg says. “And a lot of people do not know the answer to that question, by the way.” As has become part of her writing process, she had her mother write her a letter about it, because “if your mom can’t give you advice, I don’t know who’s going to give you advice.”

The answer is frustrating in its simplicity. “My grand conclusion was that it was just about taking responsibility for your actions, and knowing why you make the choices you make,” she says. And then she backtracks a little. “Really, nobody knows. Nobody has the answers! Let’s just be kind and good and communicative with each other. Let’s just start with that.”

Rachel Sugar is a writer living in New York.