A book curse was the most widely employed and effective method of discouraging the thievery of manuscripts during the medieval period. The use of book curses dates back much further, to pre-Christian times, when the wrath of gods was invoked to protect books and scrolls. The earliest known book curse can be traced to Ashurbanipal, King of Assyria from 668 to 627 BCE, who had the following curse written on many or all of the tablets collected at the library at Ninevah, considered to be the earliest example of a systematically collected library:
I have transcribed upon tablets the noble products of the work of the scribe which none of the kings who have gone before me had learned, together with the wisdom of Nabu insofar as it existeth [in writing]. I have arranged them in classes, I have revised them and I have placed them in my palace, that I, even I, the ruler who knoweth the light of Ashur, the king of the gods, may read them. Whosoever shall carry off this tablet, or shall inscribe his name on it, side by side with mine own, may Ashur and Belit overthrow him in wrath and anger, and may they destroy his name and posterity in the land.
Another book curse from the medieval ages as follows: For him that stealeth, or borroweth and returneth not, this book from its owner, let it change into a serpent in his hand and rend him. Let him be struck with palsy, and all his members blasted. Let him languish in pain crying out for mercy, & let there be no surcease to his agony till he sing in dissolution. Let bookworms gnaw his entrails ... when at last he goeth to his final punishment, let the flames of Hell consume him forever.
Another curse from Ninevah states: "Whoever removes [the tablet], writes his name in the place of my name, may Ashur and Ninlil, angered and grim, cast him down, erase his name, his seed, in the land.  Other book curses were more discreet: “He who fears Anu, Enlil, and Ea will return it to the owner’s house the same day” and “He who fears Anu and Antu will take care of it and respect it”. 
Because these tablets were made of clay, and thus easily vandalized, there were specific curses to protect against such acts such as “In the name of Nabu and Marduk, do not rub out the text!” Nabu was the Babylonian god of writing and wisdom, son of Marduk and Sarpanitu. A more detailed curse to prevent vandalism went as follows:
He who breaks this tablet or puts it in water or rubs it until you cannot recognize it [and] cannot make it to be understood, may Ashur, Sin, Shamash, Adad and Ishtar, Bel, Nergal, Ishtar of Ninevah, Ishtar of Arbela, Ishtar of Bit Kidmurri, the gods of heaven and earth and the gods of Assyria, may all these curse him with a curse that cannot be relieved, terrible and merciless, as long as he lives, may they let his name, his seed, be carried off from the land, may they put his flesh in a dog’s mouth”.
In their medieval usage, many of these curses vowed that harsh repercussions would be inflicted on anyone who appropriated the work from its proper owner. The punishments usually included excommunication, damnation, or anathema. Excommunication was the lightest of the curses because, in the Medieval Catholic Church, it was a reversible state. Both excommunication and anathema required identification of the guilty party as well as action on the part of the Church. Damnation had the benefit of not requiring human intervention as it was a state that the Creator, not the Church, visited instantly upon the soul of the perpetrator. All three types of curses were considered to be effective deterrents against the book thief.
At the time, these curses provided a significant social and religious penalty for those who would steal or deface books, which were all considered to be precious works before the advent of the printing press.
One example of a book curse in the Benedictine nuns monastery of Sant Pere de les Puel·les in Barcelona reads as follows:
For him that stealeth, or borroweth and returneth not, this book from its owner, let it change into a serpent in his hand and rend him. Let him be struck with palsy, and all his members blasted. Let him languish in pain crying out for mercy, and let there be no surcease to his agony till he sink in dissolution. Let bookworms gnaw his entrails ... when at last he goeth to his final punishment, let the flames of Hell consume him forever and aye.
Most curses were written in the book's colophon by the medieval scribe. This was the one place in a medieval manuscript where a scribe was free to write what he wished so book curses tend to be unique to each book.
A significant subset of the book curse is the document curse. These curses were employed in much the same way as the book curse, but with one significant difference; while book curses almost always protected the physical book, document curses were generally worded to protect the text of the document that contained them (Danet, 1992 p. 142). They were often found in wills, grants, charters and sometimes in writs.
- Casson, L. (2001). Libraries in the ancient world. New Haven: Yale University Press, p.12
- Casson, 2001, p.13
- Casson, 2001, p.13
- Lurker, Manfred (2004). The Routledge Dictionary of Gods, Goddesses, Devils & Demons. Routledge. p. 131. ISBN 9780203685259.
- Casson, 2001, pp. 13-14
- Basbanes, Nicholas A. (1995). A Gentle Madness: Bibliophiles, Bibliomanes, and the Eternal Passion for Books, Owl Books, 35. ISBN 0-8050-6176-2.
- Ploughing the Parchment: European Manuscripts from the Middle Ages, 500-1500. URL accessed 2 March 2006.
- Anderson, Sandra (2003). "Bibliomania and the Medieval Book Curse." URL accessed 3 May 2008.
- Danet, Brenda and Bryna Bogoch. ""Whoever Alters this, may God Turn His Face from Him on the Day of Judgment": Curses in Anglo-Saxon Legal Documents." The Journal of American Folklore 105, no. 416 (Spring, 1992): pp. 132–165.