The article reviews scholarship on Leonardo da Vinci during the 20th century. An initial fascination with a handful of paintings has led to a nearly comprehensive understanding of his art. A catalogue raisonnée for Leonardo and his school has yet to be made. Awareness of Leonardo as a scientist began with a vague reputation of a universal genius who never finished anything. Some praised, others sought to limit him as an artist-engineer. The 20th century revealed that Leonardo made substantial contributions in the domains of physics, mechanics, optics, perspective and medicine. Even so, nearly 500 years after his birth, much remains to be done in understanding fully one of the great geniuses of all time.