Mona Lisa is now officially recognized as Lisa Gherardini, wife of the Florenitne silk merchant Francesco del Giocondo.
The portrait was commissioned to Leonardo in 1503 for celebrating the second family's newborn son, and it's thought that Leonardo finished it only in France, shortly before he died in 1519.
For the newbies like me, there is an interesting video on youtube explaining why the Mona Lisa is one of the most famous paintings in history.