What is the consensus algorithm used by Cardano?

Cardano uses the Ouroboros consensus algorithm.

Ouroboros is a family of proof-of-stake protocols developed for Cardano. Instead of relying on energy-intensive mining, it allows participants to help secure the blockchain by delegating or committing stake. The protocol selects stake pools and other participants to produce blocks during scheduled periods, while the network verifies the resulting chain.

The name comes from the ouroboros, an ancient symbol of a serpent eating its own tail. An academic team led by Aggelos Kiayias presented the original Ouroboros design in 2017, describing it as a provably secure proof-of-stake protocol. Later versions were created for different security and participation requirements.

“Proof of stake” is a correct broad description of Cardano’s approach, but it is not the single named algorithm this question asks for. Ouroboros is the specific protocol family. Cardano has used successive variants, including Ouroboros Classic, Ouroboros BFT, and Ouroboros Praos; the variant matters technically, but the canonical quiz answer remains Ouroboros.