Photons -- Light Quanta

The purpose of this article is to show that the standard method of introducing the quantum description of the electromagnetic field -- by canonical field quantization -- is not the only one. We have chosen instead as the starting point the relativistic quantum mechanics of photons. Our present understanding of the nature of photons significantly differs from what has been known years ago when the concept of a photon has only been emerging. We show how the description of photons treated as elementary particles merges smoothly with the classical description of the electromagnetic field and leads finally to the full theory of the quantized electromagnetic field.