The question is a simple: How did Leonardo Da Vinci's Mona Lisa become the most famous artwork in the world. How did this small Renaissance artwork become the one painting that even Homer Simpson would have heard of? The answer, however, is not simple at all. Painted in 1503, it's a 400 year old tale full of missing pieces, contradictions, competing theories, tall tales, coincidences and puzzles. Barbara Nichol traces its path to a unique global celebrity.