In 1994, after working on the book for two years, Sabuda was finally satisfied, so he offered it to a publisher. "We love this book; we just don't know how to proceed with it," he recalls being told. It was too complicated and, because pop-up books are made by hand, too expensive. No children's books were priced at $20.

Undeterred, he took it to another publisher, who agreed to try producing the book. The result, which hit stores in 1994, was an instant classic and an engineering marvel. It became the children's book that adults put on the coffee table. Publishers Weekly dubbed him the Prince of Paper, while another reviewer called him the foremost visionary in the field.

"With The Christmas Alphabet, [Sabuda] really established a whole new standard for paper engineering," says Ann Montanaro, a Rutgers University library administrator and the founder of the Movable Book Society, an organization of pop-up enthusiasts. "His work is much more complex than previous paper engineers', and it has an artistic quality to it that few others have had."

Since then, in books ranging from Alice's Adventures in Wonderland and The Wonderful Wizard of Oz to The Night Before Christmas and Young Naturalist's Pop-Up Handbook: Butterflies, Sabuda and his sometime collaborator, Matthew Reinhart, have continued to shatter boundaries. In Alice, the final pages feature an elaborate arch of cards. In Oz, a balloon ferrying the wizard rises above one spread. In The Night Before Christmas, Santa's eight reindeer fly out of the book toward the reader.

The latest additions to the duo's catalog are Winter's Tale, an original story by Sabuda about animals, inspired by his childhood winters in Michigan; Reinhart's retelling­ of Cinderella; and a collaboration, Encyclopedia Prehistorica: Dinosaurs. Dinosaurs may be their most ambitious set of pop-ups yet. On one page, a spike-studded ankylosaurus prowls, while on another, a toothy Tyrannosaurus rex menaces the reader.

Sabuda looks back and sees his naïveté as an asset when he began creating The Christmas Alphabet. "I knew nothing about nothing," he says. "No one had said there are only 10 mechanisms to make pop-ups. There were no bounds to what you could do."

That's why his work is unique. He has never been constrained by the strictures of the genre. Where others see impassable boundaries, he sees design opportunities. "The Christmas Alphabet in itself was so nontraditional that it set the tone for the level of freedom that now exists in pop-up books," Sabuda says.

Montanaro says Sabuda is one of perhaps a dozen paper engineers working today, and one of only a few able to make a living at his passion. And she says that while the books are owned by many children, it's adults who fully understand the remarkable engineering that goes into each one. "Robert's books really shifted the marketing from strictly children to adults and collectors."