!flux11 What is the most expensive book ?

The most expensive book ever sold is considered to be "The Codex Leicester" by Leonardo da Vinci. It was purchased by Bill Gates in 1994 for $30.8 million. The Codex Leicester, which consists of a collection of largely scientific writings by da Vinci, was written between 1506 and 1510.

Highly valuable books can also include first editions of extremely popular or significant works, like "Tales of Beedle the Bard" by J.K. Rowling (which fetched £1.95 million / $2 million at auction), or rare, historically significant texts like the first edition of Shakespeare's First Folio, which, if in near-perfect condition, might fetch over $5 million.

Keep in mind that prices can fluctuate, especially with unique items like rare books, based on the collector's market, condition of the book, provenance, historical significance, and other factors.