What is the name of Leonardo's notebook that was purchased by Bill Gates in 1994?

The name of Leonardo’s notebook purchased by Bill Gates in 1994 was the Codex Leicester. It is a collection of scientific writings and drawings by Leonardo da Vinci, especially concerned with water, astronomy, geology, fossils, and the movement of air and light.

Leonardo assembled the material around 1506–1508, writing in his characteristic mirror script on loose sheets. The manuscript was later known by several names. It was called the Codex Leicester after Thomas Coke, the Earl of Leicester, acquired it in the eighteenth century, and the Codex Hammer after industrialist Armand Hammer bought it in 1980.

Christie’s auctioned the codex in New York on November 11, 1994, when Bill Gates purchased it. Gates had the pages digitally scanned, helping make Leonardo’s ideas accessible through computer screensavers and a CD-ROM. The manuscript remains privately owned but is periodically displayed publicly.

A common mix-up is the Codex Atlanticus, another major Leonardo collection held by the Biblioteca Ambrosiana in Milan. The Codex Forster and Codex Trivulzianus are also genuine Leonardo manuscripts, but neither was the notebook bought by Gates.