U.S. writer Madeleine L'Engle, beloved for her classic science-fiction classic A Wrinkle in Time, has died, her publicist said Friday. She was 88.

L'Engle died Thursday of natural causes at a nursing home in Litchfield, Conn.

Author Madeleine L'Engle, in an undated photo, became fascinated with quantum physics before writing A Wrinkle in Time.
(Farrar, Straus and Giroux/Associated Press)

L'Engle is the author of more than 60 books, including works for both children and adults.

But she is best known for A Wrinkle in Time, which won the 1963 Newbery Medal for excellence in children's literature and has never been out of print since its publication.

The novel, which tells the story of an adolescent girl and her genius brother who search across the universe for their missing father, was rejected by dozens of publishers.

L'Engle wrote the book after developing an interest in quantum physics, particularly Einstein's theories on the nature of time.

Some of her other books included references to scientific subjects such as tesseracts and mitochondrial DNA, but she also wrote memoirs, poetry and short stories.

She wrote several books involving the characters she created for Wrinkle, including 1973's A Wind in the Door, 1978's A Swiftly Tilting Planet and 1986's Many Waters.

Though her books appealed to young people, she never considered herself a children's author.

'I never write for any age group': L'Engle

"In my dreams, I never have an age," she said. "I never write for any age group in mind. When people do, they tend to be tolerant and condescending and they don't write as well as they can write.

"When you underestimate your audience, you're cutting yourself off from your best work."

Born in New York on Nov. 29, 1918, she was educated at Smith College and published her first short stories while still in college.

She lived in Greenwich Village in 1941 and there met her husband, actor Hugh Franklin.

Her first book, The Small Rain, was published in 1945, followed by Ilsa in 1946.

She and Franklin moved to an old farmhouse in Connecticut and operated a general store while L'Engle wrote. The couple had three children.

She published two more novels but didn't achieve success until 1963, when she and Franklin moved back to New York and he landed a plum role on a soap opera.

That same year, A Wrinkle in Time was published to critical acclaim and lasting commercial success.

L'Engle won the Newbery Honour for A Ring of Endless Light in 1981.

One of her books for adults, Two-Part Invention, was a memoir of her marriage, completed after her husband's death from cancer in 1986.

Deeply involved in community and church, she also served as writer-in-residence at the Cathedral Church of Saint John the Divine in New York.

Her Genesis trilogy, including 1983's And It Was Good, 1986's A Stone for a Pillow and 1989's Sold Into Egypt are based on biblical characters.

Last book published in 2001

Asked why anyone tells stories, L'Engle said the motivation is often faith.

"It does indeed have something to do with faith — faith that the universe has meaning, that our little human lives are not irrelevant, that what we choose or say or do matters, matters cosmically," she said.

L'Engle continued to write both fiction and non-fiction until 2001. She also taught and lectured widely, and was for two years president of the Authors Guild.

Her last book, published in 2001, was a children's book, The Other Dog.  In 2004, U.S. President George W. Bush awarded her a National Humanities Medal.

With files from the Associated Press