I have heard theories that it is actually Leonardo himself, disguised as a woman. Also, that the portrait is really a composite of many of the women he sketched, painted, etc... It's all speculation!!

I've read it in a book that although Mona Lisa's identity is not certain, she might either be the wife of one of Da Vinci's friends or some servant girl. This theory about her having been Da Vinci's grandmother wasn't familiar to me. But who knows?

The Mona Lisa was given her name by Vasari...he was the one who wrote biographies of DaVinci, Michaelangelo, etc. The first art historian, in fact,
Lisa was the wife of an Italian merchant, quite wealthy, and Mona roughly translates as Madame, or married woman.
"Leonardo undertook to execute, for Francesco del Giocondo, the portrait of Mona Lisa, his wife; and after toiling over it for four years, he left it unfinished; "
http://www.fordham.edu/halsall/source/vasari1.html

Specialists who studied new high-tech images of the "Mona Lisa" believe Leonardo da Vinci's model may have been pregnant or have recently given birth when she posed for him. The clue was something she was wearing.

Scans turned up evidence of a fine, gauzy veil around Mona Lisa's shoulders — a garment that women of the Italian Renaissance wore when they were expecting, leading French museum researcher Michel Menu said in an interview Wednesday.

As the painting aged, the veil darkened. The thick, dark varnish on da Vinci's 16th-century masterpiece makes it hard even to know what color her dress is — writers have called it everything from black to brown to green. A piece of fabric draped over Mona Lisa's shoulder was sometimes interpreted as a shawl or a scarf.

But images obtained from infrared reflectography, taken in 2004, tell a different story. The veil — called a guarnello — is transparent, and it looks similar to a gauzy garment in Sandro Botticelli's "Portrait of a Lady," depicting a pregnant woman with her hand over her stomach.

Tradition holds that the "Mona Lisa" is a painting of Lisa Gherardini, wife of Florentine merchant Francesco del Giocondo, and that da Vinci started painting it in 1503. In France, the painting, on display at the Louvre Museum, is referred to as La Joconde — the French version of her married name. The name Mona Lisa is the equivalent of "Madam Lisa."

The veil "would confirm art historians' hypothesis that Giocondo asked for a painting of his wife to celebrate the birth of his second son," said Menu, chief of the research department at the French Museums' Center for Research and Restoration, which has its offices in the Louvre.

art scholars have been asking this question for centuries with no real definitive answers. you'll find all sorts of crazy theories out on the net., especially with the popularity from the recent movie about leonardo. i saw the original in paris last spring, and it is quite a moving experience. i simply enjoy the painting for what it is and try not to get caught up in all the hype about it. in my opinion, it is not the most spectacular painting to begin with. i am actually a bigger fan of michelangelo's work

I dunno the craziest thing I have heard I read in a book about the guy that used a wrong solvent when restoring it and wiped off Mona Lisa's eyebrows for the rest of history. It was the last detail DaVinci put on. And yeah... That would suck to be the guy that wiped off her eyebrows, ha.