Wanda Gag was an American artist, author, and illustrator best known for Millions of Cats, a picture book whose flowing images and rhythmic storytelling helped transform children's publishing. Usually styled Wanda Gág, she brought the skills of a printmaker and draftsman to the page. Her books make pictures and words partners in the telling of a story.

Gág grew up in an artistic family in Minnesota and pursued formal art training before developing a career in New York. She worked in drawing and printmaking as well as children's literature, gaining recognition for both. Her published diaries, gathered in Growing Pains, offer a record of the ambitions, difficulties, and close observation that shaped her development.

Millions of Cats turns a simple search for a companion into an exuberant procession across hills and valleys. Other books and her illustrated translations of Grimm's tales show a continuing interest in folktale patterns, expressive line, and imaginative transformations. Her work received both Newbery and Caldecott honors. Gág's lasting achievement lies in treating the picture book as an integrated work of art, designed to reward listening, looking, and repeated discovery.