Isleworth Mona Lisa
According to Leonardo's early biographer Giorgio Vasari, Leonardo had started to paint "Mona Lisa" in 1503, but "left it unfinished". However, a fully finished painting of a "certain Florentine lady" surfaced again in 1517, shortly before Leonardo's death and in his private possession. The latter painting almost certainly is the one that now hangs in the Louvre. Based on this contradiction, supporters of the authenticity of the "Isleworth Mona Lisa" claim it is the unfinished "Mona Lisa", made at least partially by Leonardo, and the Louvre "Mona Lisa" a later version of it, made by Leonardo for his own use.
Mona Lisa
Before that discovery, scholars had developed several alternative views as to the subject of the painting. Some argued that Lisa del Giocondo was the subject of a different portrait, identifying at least four other paintings as the "Mona Lisa" referred to by Vasari.
Several other women have been proposed as the subject of the painting.
Isabella of Aragon, Cecilia Gallerani, Costanza d'Avalos, Duchess of Francavilla, Isabella d'Este, Pacifica Brandano or Brandino, Isabela Gualanda, Caterina Sforza—even Salaì and Leonardo himself—are all among the list of posited models portrayed in the painting.
The consensus of art historians in the 21st century maintains the long-held traditional opinion, that the painting depicts Lisa del Giocondo.