Although the wave-particle duality is one of the conceptual cornerstones of quantum mechanics, the waveor- particle dillemma limited to light only is at least 250 years older than the quantum branch of physics. The question of the nature of light has been an important scientific issue since the 17th century, the same time when modern optics was born. One can easily discern three different stages in the evolution of this
problem, and to each of these stages we can attach names of several famous physicists who contributed to our understanding of light. Their discussions and different explanations demonstrate how baffling the nature of light has seemed from the beginning, and how rich is the current of thoughts and ideas that it has stimulated. Only in the last century, thanks to the quantum theory, did the duality problem unexpectedly expand to embrace matter as well.