The first folio was one of several items stolen in 1998
A man has been bailed by police after being detained over the theft of the "most important book in the English language" that was stolen 10 years ago.
The 1623 first folio (wide-paged book) of a collection of works by William Shakespeare could be worth £15m.
It was one of a number of literary works taken from Durham university in December 1998.
Police said the suspect, aged 51, allegedly asked a library in the US to value the work.
The unnamed man was bailed after being questioned at Durham City police station.
A Durham Police spokesman said a man, claiming to be an international businessman who had acquired the volume in Cuba, showed it to staff at the Folger Shakespeare Library in Washington DC and asked them to verify it was genuine.
He agreed to leave it with librarians, whose research revealed it to have been stolen.
It was one of the first collected editions of Shakespeare's plays printed. Only between 200 and 300 copies are thought to have survived around the world.
A spokesman for Durham University said staff were "rejoicing" following the recovery of the book, described by experts as "the most important book in the English language" at the time of its theft.
The man was arrested on Thursday at an address in Wigeon Close, Washington, Tyne and Wear, after the British Embassy in the US alerted Durham Police to the find two weeks ago.
The stolen items were part of an exhibit of 50 examples of English literature dating from the Middle Ages to the 20th Century.
Other items taken in the university raid included a handwritten manuscript of an English translation of the New Testament from the 14th Century.
Also stolen was a book by 10th Century scholar Aelfric, written in 1566, a first edition of Beowulf from 1815 and a handwritten manuscript from the early 15th Century containing a fragment of a poem by Canterbury Tales author Geoffrey Chaucer.
The Durham Police spokesman said officers were working with the FBI in the United States.
Bill Bryson, chancellor of Durham University and author of an acclaimed book on Shakespeare, said: "This is not only wonderful news for Durham University but for all Shakespeare's scholars and fans around the world, of which I am most definitely one.
"Like Shakespeare himself, this book is a national treasure giving a rare and beautiful snapshot of Britain's incredible literary heritage."
The Shakespeare first folio was acquired by John Cosin, former Bishop of Durham, and was part of the library he established in Durham in 1669.
University vice-chancellor, Prof Chris Higgins, added: "Our security has been very significantly reviewed and enhanced to the highest standards since the theft 10 years ago and we are confident the first folio will be safe when it arrives back in Durham."