Since the discovery of electromagnetic radiation by Maxwell and Hertz in the 19th century, light has been our preferred information carrier. Little it was known to them that the quantum revolution of the 20th century would, once again, reshape our understanding of light and unlock new ways of communicating and calculating. Photons and the newly discovered laws of quantum mechanics (uncertainty, wave-function collapse, Bell inequalities…) enabled new cryptographic protocols and computation algorithms. In this colloquium, we review some of the applications of photons in secure quantum communications and information processing. In communication, they allow for fast transmission of information and, if attenuated to the few photons level, we can use quantum mechanics to establish new cryptographic protocols or transmit quantum information. In computation, however, light is trickier than other systems since photons do not interact between them (in first order). A deeper theoretical understanding of optical circuits is required to accompany the recent experimental advances if quantum optics is to be regarded as a viable computational technology.​

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