Lightweight symmetric cryptography emerged thirty years ago with the proliferation of applications with very limited resources, such as energy-harvesting devices, like RFID tags. These platforms actually imposed severe constraints on the algorithms that they can embed, and standardized cryptographic algorithms appeared to be too expensive in such contexts. This situation led the industry to design proprietary ciphers for wireless access control or public transport ticketing systems, which met the implementation requirements, typically a very small hardware footprint and very low power consumption. Some examples include KeeLoq used for car keyless entry systems or Crypto-1 integrated in the MIFARE Classic RFID contactless smart cards. However, designing a symmetric cipher, even a lightweight variant of an existing cipher, is not a trivial task: all these early attempts were severely broken, which was a major concern for such widely deployed devices. It then became clear that lightweight cryptography needed to take advantage of the expertise of the cryptography community, especially of the comprehension of symmetric algorithm design that was gained during several public competitions. A new research direction then emerged, related to lightweight primitives, resulting in several new design principles and in many algorithms. The multiplication of proposals and the need for reliable primitives which received an in-depth security evaluation led to the inclusion of a lightweight category in several design competitions such as eSTREAM (2004-08) for stream ciphers and CAESAR (2014-19) for authenticated encryption. More recently, a dedicated standardization effort launched by NIST in 2019 led to the selection of Ascon as a future standard.