Block books, also called xylographica or chiroxylographies, are short books of up to 50 leaves, block printed in Europe in the second half of the 15th century as woodcuts with blocks carved to include both text and illustrations.
The content of the books was nearly always religious, aimed at a popular audience, and a few titles were often reprinted in several editions using new woodcuts.
Although many had believed that block books preceded Gutenberg's invention of movable type in the first part of the 1450s, it now is believed that most of the surviving block books were printed in the 1460s or later, and that the earliest surviving examples may date to about 1451.
Chiroxylographies seem to have functioned as a cheap popular alternative to the typeset book, which was still very expensive at this time.
Single-leaf woodcuts of chiroxylographies from the preceding decades often included passages of text with prayers, indulgences and other material; the block book was an extension of this form.
Block books or chiroxylographies are very rare and there are apparently some editions surviving only in fragments, and many probably not surviving at all.