A chapbook is a small publication of up to about 40 pages, sometimes bound with a saddle stitch.

In early modern Europe a chapbook was a type of printed street literature. Produced cheaply, chapbooks were commonly small, paper-covered booklets, usually printed on a single sheet folded into books of 8, 12, 16 and 24 pages. They were often illustrated with crude woodcuts, which sometimes bore no relation to the text (much like today's stock photos), and were often read aloud to an audience. When illustrations were included in chapbooks, they were considered popular prints.

The tradition of chapbooks arose in the 16th century, as soon as printed books became affordable, and rose to its height during the 17th and 18th centuries. Many different kinds of ephemera and popular or folk literature were published as chapbooks, such as almanacs, children's literature, folk tales, ballads, nursery rhymes, pamphlets, poetry, and political and religious tracts.

The term "chapbook" for this type of literature was coined in the 19th century. The corresponding French term is bibliothèque bleue (blue library) because they were often wrapped in cheap blue paper that was usually reserved as a wrapping for sugar. The German term is Volksbuch (people's book). In Spain they were known as pliegos de cordel (cordel sheets). In Spain, they were also known as pliegos sueltos, which translates to loose sheets, because they were literally loose sheets of paper folded once or twice in order to create a booklet in quarto format. Lubok is the Russian equivalent of the chapbook.

The term "chapbook" is also in use for present-day publications, commonly short, inexpensive booklets.