For 15 years, author-illustrator Marla Frazee and Allyn Johnston, v-p and publisher of Beach Lane Books, an imprint of Simon & Schuster, have collaborated on inspired children’s books. Their latest release, The Farmer and the Clown, a wordless book acclaimed for its emotional depth, was released in September 2014.

Their first collaboration came when Johnston tapped Frazee to illustrate Harriet, You’ll Drive Me Wild!, by Mem Fox (Harcourt), back in 2000. “I’d long admired Marla’s illustrations for their emotional heart, humor, irresistible detail, and visual storytelling excellence,” Johnston says. She also thought that Frazee, the mother of three boys, might relate to the book, which is about a mom losing her temper after spending a long day at home with a young child. “This was right up my alley at the time,” Frazee says.

Even before they worked together, the pair became fast friends, bonding over their love of children’s books and the importance of these books to their roles as mothers. “We discussed picture books from a professional vantage point, too: what inspired us and frustrated us,” Frazee says. “It was all very cathartic and forged the foundation of our future collaboration.”

]After the release of Harriet, their professional relationship “moved forward organically,” Johnston says. She brought in Frazee to illustrate Susan Myers’s Everywhere Babies (2001).

Afterward, Frazee wrote her first book, Roller Coaster (2003), which led to a new collaborative phase, where “Marla’s art and text [were] the focus of our editorial discussions,” Johnston says. “I loved the very simple, dry, direct writing in her story and how much room the words left for her to widen the narrative in her pictures. Manuscripts this spare and strong are rare items.”

Frazee continued to illustrate books for others, but she also wrote her own as well: Walk On!; Santa Claus: The World’s Number One Toy Expert; A Couple of Boys Have the Best Week Ever; The Boss Baby; and Boot & Shoe.

Since their collaboration began, Frazee has picked up two Caldecott Honors for illustration—one for A Couple of Boys, the other for All the World, written by Liz Garton Scanlon.

The pair say their creative process varies from book to book and depends on the nature of each project. “Sometimes I don’t see much of anything until she has a more or less complete tight dummy,” Johnston says. “Other times I see a tiny, rough, faint, 32-page thumbnail map all laid out on one 8½ × 11 in. sheet of paper that has scribbles for placeholders.”

For their current collaboration, Frazee is illustrating a book written by poet Victoria Chang, which they’ve been trying to work into their project rotation since 2009. Frazee turned to “old technology”—manila paper, tempera paint, cheap school supply brushes—to work on the images for the book. During this process, she and Johnston communicated via text messages.

Johnston says that when working with someone “as experienced as Marla,” she merely provides guidance during the creative process. “I think of my role as asking a bunch of questions both easy and hard to get us both thinking,” she says. “One of the most inspiring things for me about Marla is her strong conviction about what she is doing in each of her books. She always has a sense of where she’s going or attempting to go, and my job is to stay out of her way until she needs a response.”