Picture books are books for young children that tell a story through illustrations and a small amount of text. Some may not have any text.
Chapter books tell a single story primarily or exclusively through text that is divided into parts called chapters.
Picture books are generally geared toward preschool- through early-elementary-aged children. Chapter books are usually intended for older children who can read on their own and do not need illustrations to aid in comprehension.
Picture books tend to be larger in size than chapter books to allow the illustrator more space for creating images, and are usually printed in full color. Chapter books tend to be smaller in size and printed in black and white since they contain mostly text.
"The Very Hungry Caterpillar" by Eric Carle is an example of a picture book that uses illustrations and minimal text. "The Adventures of Polo" by Regis Faller is a picture book with no text. "A Wrinkle in Time" by Madeliene L'Engle is an example of a chapter book.