Illustration is usually pictorial material appearing with a text and amplifying or enhancing it. Although illustrations may be maps, charts, diagrams, or decorative elements, they are more usually representations of scenes, people, or objects related in some manner - directly, indirectly, or symbolically - to the text they accompany.

The historical origins of illustration are as ancient as those of writing. The pictographs of early humans, and the hieroglyphics of such early civilizations as the Egyptian, contain the roots of both illustration and text. Illustrated children's books, which would ultimately account for the major portion of all illustrated books, grew steadily in numbers during the 19th century, especially in England and the United States. Most of the contemporary illustrated books are those produced for children.