One of the most valuable and coveted books in the world, the First Folio was uncovered when librarian Remy Cordonnier dusted off a book of Shakespeare's works dating to the 18th century for an exhibition on English literature in the town of Saint-Omer near Calais.
"It occurred to me that it could be an unidentified First Folio, with historic importance and great intellectual value," he told AFP.
"It is the 231st copy found in the world and the second in France," said Cordonnier.
The book, a compilation of 36 of Shakespeare's plays, is in good condition but missing about 30 pages, including the title page, which could explain how it went unnoticed for centuries.
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Rasmussen wrote a book on the First Folio called "The Shakespeare Thefts" detailing his thrilling global hunt for what remains of the initial 750 copies of the book, a favourite for thieves across the centuries.
Rasmussen's book speaks of several First Folios which have had pages ripped out of them, and one with a bullet lodged in it.
The Folger Shakespeare Library in Washington, which houses the largest collection of Shakespeare material, says on its website that the First Folio is the only source for 18 of Shakespeare's plays, including Macbeth, "which would otherwise be lost."
It is believed that the copy found in France was taken to Saint-Omer by English refugees from Anglican persecution, said Cordonnier.
However she said France would not sell the book, and that it would be stored in the library's safe with other precious items.