Lionni became the first children's author/illustrator to use collage as the main medium for his illustrations. Reviewers such as "Booklist" and "School Library Journal" have said that Lionni's illustrations are "bold, sumptuous collages" that include "playful patches of color" and that his "beautifully simple boldly graphic art [is perfect to share with very young children." "Book World" said that "the translucent color of the pictures and the simplicity of the text make a perfect combination." Many of Lionni's books deal with issues of community and creativity, and the existential condition, rendered as fables which appealed to children. He participated in workshops with children and even after his death school children continue to honor him by making their own versions of his books.