Leonardo da Vinci's viola organista was a keyboard instrument that used a bowing mechanism to sound strings.
Leonardo drew several versions of the instrument during the late 15th century. Pressing a key would move a string against a rotating wheel or other continuously moving bowing surface. This allowed a performer to control pitched strings from a keyboard rather than holding a bow by hand.
The concept combined the keyboard action of an organ or clavichord with the bowed-string principle of instruments such as the viola. Leonardo was interested in making complex musical effects easier to coordinate, and his sketches show changes in the mechanism across different designs.
No surviving evidence proves that Leonardo completed a working viola organista. Modern builders have constructed instruments from his drawings, but their mechanisms are reconstructions rather than original Renaissance examples. The name is modern and descriptive; Leonardo's notebooks contain the designs, but they do not establish a single finalized instrument built by him.