Charlesbridge could be the turtle in the publishing race. It has stayed the course with careful publishing and steady growth since its founding in Watertown, Mass., in 1989. Over the past five years it has averaged 5% growth annually, according to president and publisher Brent Farmer.

The press’s list reflects a similar steadiness of purpose as well as Farmer’s belief in publishing content of lasting value and being “a trusted steward” of the intellectual property of authors, illustrators, and agents. Eighty percent of the books Charlesbridge has published over the past 25 years remain in print. That figure includes 29 of its first 30 books, among them Jerry Pallotta’s alphabet books, Alexandra Wright’s Will We Miss Them? on endangered species, and Virginia Kroll’s Wood-Hoopoe Willie on diversity. Those books and authors continue to be key to Charlesbridge; excluding sales through book clubs, Charlesbridge has sold more than 3.6 million copies of Pallotta’s books. In March, it will release his latest work, Butterfly Counting, illustrated by Shennen Bersani.

But steady in no way implies an unwillingness to adapt and change. Arguably, the past five years have marked some of the press’s biggest transitions, including its purchase of Imagine Publishing in July 2010, which gave Charlesbridge its first adult titles – up to then it had only published books for children – and its first New York Times bestsellers under Imagine’s Peter Yarrow imprint.

The imprint may be known for its picture-book editions of classic children’s songs with accompanying CDs. In November that, too, will change with the publication of Yarrow’s own adult book, Peter Paul and Mary: Fifty Years in Music and Life (Nov.), a photographic look back at the trio that helped define the ’60s, cowritten with Noel (Paul) Stookey and Mary Travers. Charlesbridge is also expecting it to be a bestseller.

One of the biggest transformations at Charlesbridge took place at the start of this year. For the first time since its founding, the privately held press moved from distributing its own books to closing its warehouse and working with Penguin Random House Distribution Services for sales and distribution. “We were a well-oiled machine going into this,” says executive v-p and associate publisher Mary Ann Sabia, who calls working with PRH “fabulous. In these past five months we’ve seen big growth in international sales and special sales.” She appreciates having a bigger sales force, especially one with seasoned adult reps for the Imagine titles.

The press started ramping up the number of titles and the mix several years ago, when it moved to 50 books a year. That figure includes 10 adult titles, mostly cookbooks, puzzles, and novelty books. Farmer would like to make “another big jump” over the next three years and increase the list to 60. Charlesbridge’s relationship with PRH should make planning for that type of growth easier. It’s already begun benefitting from its backlist of 540 children’s titles, two-thirds of which are nonfiction; many are taking on new life under Common Core, Sabia says.

While Charlesbridge is committed to publishing picture books, part of the increase in titles will come from middle grade. At present it publishes two middle grade books a year and will double that number to four in 2015. Although it doesn’t publish YA and has no plans to, Mitali Perkins’s Bamboo People was a 2010 Indies Choice Young Adult Honor Book. Her next middle-grade novel, Tiger Boy, which takes place in contemporary Bangladesh, is due out in March.

Other forthcoming books include the launch of a new series on the STEAM philosophy of learning, which is illustrated by Peter H. Reynolds, and written by his twin brother, Paul A. Reynolds, Full STEAM Ahead (Sept.). In April, Imagine will publish a picture-book edition of Lewis Carroll’s Alice in Wonderland in honor of its 150th anniversary, edited by Joe Rhatigan and Imagine founder and former Sterling CEO Charles Nurnberg, illustrated by Eric Puybaret.

Looking back, Sabia credits the authors and illustrators as well as the staff, many of whom have been there for a decade or more, for the house’s success. She herself has been with Charlesbridge from the beginning. “What a wonderful ride,” she says. “I can’t wait to see what the next 25 years have in store for Charlesbridge – and the publishing industry as a whole.”