Leonardo da Vinci (1452-1519) has evoked two fundamentally different responses: one sees him as central to early modern science, another dismisses him as an eccentric with no influence. Both views were found while he was still alive. Twentieth century scholars such as Marie Boas Hall argued that because he never published he had no influence, while one recent scholar has dismissed him as "an ingenious empiricist working in an intellectual vacuum.Was Leonardo merely a recluse working on his own out of touch with the great traditions; an over ambitious amateur making notes without any underlying method and structure? This little book shows that Leonardo was widely read and in contact with some of the major scholars of his day. A survey is made of his extant treatises to confirm that these are much more structured than is at first apparent. His plans for books are examined to discern how he intended to arrange his material. It is shown that for all his universality Leonardo focussed on a surprisingly small number of basic themes; that although Leonardo's study of the natural world includes physics, biology and botany he treats them all in terms of mechanics. A detailed reading of his notebooks reveals that he was guided (and inevitably sometimes misguided) by a clear method. The notebooks also contain proof that Leonardo did not write them solely for private study; that he specifically intended them for other readers and had plans for publication. Finally, it will require a survey of historiography to understand how all all this could have been forgotten, with the result that scholars have claimed that he was a peripheral figure, when in fact Leonardo's method is of central importance to the western tradition.In 1973-1974 the late Dr. Kenneth D. Keele, M.D., F.R.C.P. and the author reconstructed some of Leonardo's descriptions of perspective in order to determine whether these had an experimental basis. It was found that they did. The possibility that they had simply been thought experiments was excluded because some of his claims were so unlikely that they had to be tested in order to make sense. The experiments led to a long term cooperation: first two years together as Senior Research Fellows at the Wellcome Institute for the History of Medicine (London); then with intermittent visits during the seven years while the author was at the Herzog August Bibliothek (Wolfenbüttel). As work progressed Leonardo's method became increasingly evident. The challenge of communicating this method inspired Dr. Keele to write Leonardo da Vinci's Elements of a Science of Man and led the author to write his Leonardo Studies I-II.Originally a lecture at the Ateneo di Brescia, "Struttura e metodo nei manoscritti di Leonardo" sponsored by the Centro di studi Leonardiani, Brescia, April, 1991. Published as a book: Brescia: Centro Ricerche Leonardiane, 1993. Revised March/April 2004. Redesigned and made available online in 2021.More information about this and other works you can find https: //www.leonardostudies.com