The notebooks are all that remain of Leonardo apart from his paintings and provide an extraordinary glimpse into Leonardo and his mind, life and emotions. Happily, more than five thousand pages of notes (about a fifth of the total that he produced) survive, written in his unmistakable mirror handwriting, going from right to left. This is the so-called "sinistrorse centrifugal writing of the left hand". Leonardo was left-handed by choice and not by necessity, and perhaps wrote in this way because of his rebelliousness against convention and a desire to be different, or perhaps simply because he wanted to hide the results of his tireless genius from indiscreet eyes.
After his death, this enormous body of writing, certainly the most substantial of the Renaissance period, was damaged by fire, stolen or vandalised. When he died, he left all the notebooks to his faithful disciple, Francesco Melzi, who looked after them carefully, but after his death his heirs began to break up this huge and immensely important body of material. Indeed, to begin with, they left the notebooks in an attic, having no understanding of its significance, and then they gave them away or sold them cheaply to friends and collectors. The seventeenth-century sculptor, Pompeo Leoni, was largely responsible for mixing up the pages and, with the intention of separating the artistic drawings from the technological ones and putting the scientific pages together, he split up part of the original manuscripts, and cut and rearranged the pages to form two large collections now known as the Codex Atlanticus and the Windsor Collection.
Following the same plan, he put together at least four fascicles. From 1637 to 1796, some of the manuscripts were kept in the Biblioteca Ambrosiana in Milan, but Napoleon on his arrival there arranged for them to be removed. Only some of these were returned to Milan in 1851, while some were kept in Paris and others in Spain, where a number of them were not found until 1966. This is why Leonardo's notebooks are so dispersed and divided now into as many as ten different codices:
- Codex Atlanticus (Milan, Biblioteca Ambrosiana)
- Windsor Collection (Windsor Castle, Royal Library)
- Arundel Codex (London, British Museum)
- Codex Institut de France (Paris, Institut de France)
- Forster Codex (London, Victoria and Albert Museum)
- Bird flight Codex (Turin, Biblioteca Reale)
- Trivulzio Codex (Milan, Biblioteca Trivulziana in the Sforzesco Castle)
- Madrid Codices (Madrid, Biblioteca Nacional)
- Leicester Codex (formerly Hammer Codex) (Seattle, Bill Gates Collection)
- Ashburnham Codex (Paris, Institut de France)