Esphyr Slobodkina's picture book, first published in 1940, tells the story of a peddler who sells caps from a stack balanced on his head—gray caps, brown caps, blue caps, and red caps, all piled above his own checked cap. When he falls asleep under a tree, he wakes to find his caps gone and a tree full of monkeys wearing them. His attempts to recover his merchandise teach problem-solving through imitation in a story whose rhythmic repetition has delighted children for generations. Slobodkina, a Russian-born artist associated with the American Abstract Artists group, created illustrations with bold shapes and limited colors that remain visually fresh decades later. The peddler's cry—'Caps! Caps for sale! Fifty cents a cap!'—has become part of American childhood's shared language. The story works because it respects children's intelligence: the solution comes not from adult intervention but from the peddler's frustrated gesture, which the monkeys copy. The monkeys' mischief is pure Id—they take what they want, ignore demands to return it, and only respond to their own imitative instincts. Young listeners identify with both the peddler's frustration and the monkeys' freedom. The book demonstrates how a simple premise, clearly executed with memorable visual style, creates a classic. Parents and teachers report that children who have heard this book a hundred times still request it again, testimony to its inexhaustible appeal.