Girdle books were small portable books worn by medieval European monks, clergymen and aristocratic nobles as a popular accessory to medieval costume, between the 13th and 16th centuries. They consisted of a book whose leather binding continued loose below the cover of the book in a long tapered tail with a large knot at the end which could be tucked into one's girdle or belt. The knot was usually strips of leather woven together for durability. The book hung upside down and backwards so that when swung upwards it was ready for reading. The books were normally religious: a cleric's daily Office, or for lay persons (especially women) a Book of Hours. One of the best known texts to become a girdle book is Boethius's The Consolation of Philosophy, although it is the only surviving philosophical/theological girdle book.

Women especially wore the girdle book out of convenience since it was already fashionable, at least in the 15th century, to wear a girdle belt above the waistline. A book secured on the girdle belt served both the utilitarian function of enabling hands-free carrying and protecting valuable books from theft and the elements. It also made a visible statement of social position, wealth and learning (or at least literacy). Authoritative figures, saints or apostles like St. Jerome were often depicted holding girdle books. Girdle books also appeared to be a fashionable accessory for lay women. Artistic depictions of the girdle book confirm their popularity as an accessory.

Girdle books first appeared in the late 13th century and gained popularity through the 15th, sometimes becoming ostentatious jewel-encrusted presentation books, and falling out of favour late in the 16th century, when printed books had become much more common. Another possible reason for their decline was the relatively small number of specialized girdle-protected texts becoming outdated with little need to replace them. In an environment of increasingly cheap printing it was simpler to replicate texts than spend time preserving individual manuscripts. The intricately constructed girdle bindings were simply impractical after a certain point.