Miniature books, commonly defined as books smaller than 3″ x 3″ (76.20 mm x 76.20 mm) in width and height, don’t get a lot of respect from many book collectors, an unfortunate circumstance since the printing of such books often requires more skill than is required for printing the typical book in the marketplace. In fact, printing such books requires so much skill that [d]uring the first centuries of printing, miniature books presented challenges to apprentices in the printing trades. Exercises in setting small types and binding diminutive volumes were instrumental in learning the profession.
Such tiny books were more popular in centuries past partly because they were easily carried or concealed (an especially important consideration if one was fleeing from religious persecution). This accounts for the numerous thumb Bibles(paraphrases prepared chiefly for children) and miniature Bibles that one occasionally still finds available at major auctions: