Albert Einstein, born in Ulm (German Empire) and employed as a third-class examiner at the Bern Patent Office, published in March 1905 — within his Annus Mirabilis — the paper 'Über einen die Erzeugung und Verwandlung des Lichtes betreffenden heuristischen Gesichtspunkt', proposing that light is not a continuous wave but propagates in discrete quanta of energy — what Gilbert Lewis would name 'photons' in 1926. Einstein starts from Planck's quantum hypothesis (1900) and radically extends it: if light energy is quantized, the photoelectric effect — the emission of electrons by illuminated metals, observed since Hertz (1887) and without classical explanation — is naturally explained. An electron can only be ejected if the incident photon has sufficient frequency, regardless of light intensity; the kinetic energy of the emitted electron is proportional to frequency, not amplitude. This radically counterintuitive prediction from the standpoint of Maxwellian wave optics was verified experimentally by Robert Millikan between 1914 and 1916 — Millikan expected to refute it and confirmed every prediction instead. The 1905 paper is the founding act of wave-particle duality and one of the pillars on which quantum mechanics is built. Its technological consequences are direct and massive: photovoltaic cells, CCD detectors, photodiodes, photomultipliers, and the photolithography used in semiconductor manufacturing all operate on the principle established in this paper. Einstein received the Nobel Prize in Physics in 1921 — awarded in 1922 — specifically for this work; the committee did not cite relativity.