Abstract: Optics is an ancient discipline through which humanity has understood nature and explored the material world. From classical geometrical optics and wave optics to the modern framework of quantum optics, our understanding of light has evolved over thousands of years. Taking the century-long development of the photon as its main thread, this article reviews the emergence, theoretical construction, and experimental verification of the quantum theory of light. It provides an in‑depth analysis of the evolutionary logic and scientific significance of core theories, including Planck’s quantization theory, Einstein’s light quantum hypothesis, and quantum electrodynamics. Furthermore, we summarize the development of core technologies involving lasers, single-photon sources, quantum entanglement, quantum key distribution, photonic quantum computation and simulation, and photonic quantum memories. We also review the achievements of China’s research teams—from following and keeping pace to taking a leading role in this field. Finally, in light of global trends in science and technology, we offer an outlook on future directions of photonic quantum technologies, providing references and insights for both fundamental research and industrial implementation.