Picture books are probably the most popular type of children's book. While there is tremendous variety among picture books, there are a few traits that distinguish the genre. For example, picture books tend to be large. Picture books feature rich illustrations. The illustrations in picture books are often as important as the text in determining the quality of the book. While picture books are written for children, they are not structured as rigidly as other genres. Consequently, children of varying ages can read and appreciate them.