The painting is a portrait and depicts a seated woman, Lisa del Giocondo, (Mona is Italian for “my lady”) the wife of a wealthy Florentine merchant, whose facial expression is mysterious. Others believe that the slight smile means that the subject is hiding a secret. The ambiguity of the subject’s expression, the monumentality of the composition, and the subtle modeling of forms and atmospheric illusionism were novel qualities that have contributed to the continuing fascination and study of the work. It is arguably the most famous portrait of all time.
Images of the Mona Lisa are ubiquitous so most people have seen it many times. Yet a viewer who seeks to understand the painting should try to see it with new eyes. What jumps out at the viewer is the uncanny way that the painting seems alive. Her eyes seem to follow our eyes. Also notice the wafer-thin veil that covers her head, suggesting a demure personality. See how the winding curves in the natural yet surreal landscape pair with the curves of Mona Lisa’s body and dress.
Leonardo used a pyramid design to place the woman simply in the space of the painting. Her folded hands form one corner of the pyramid. Her breast, neck and face glow in the same light that models her hands. The light gives the variety of living surfaces an underlying geometry of spheres and circles. Leonardo referred to a basic formula for seated female figure: the images of seated Madonna, which were widespread during the Renaissance. He modified this formula in order to create an impression of distance between the sitter and the observer. The armrest of the chair functions as a dividing element between Mona Lisa and the viewer.
Da Vinci used the technique of sfumato to create shadowy areas where one shape blends into another. Some critics attribute the seeming abilty of the painting to change to sfumato.
As mentioned before, da Vinci depicted Mona Lisa much like the Madonna, i.e. the Virgin Mary (Hadhrat Maryam). Some contend that he was also inspired by the memory of his own mother, Caterina.
If you have the time and the interest, you can find many theories about the Mona Lisa online. There are also many parody pieces.
E.H. Gombrich, The Story of Art, http://www.amazon.com/The-Story-Art-E-H-Gombrich/dp/0714832472/