Ouroboros is a groundbreaking blockchain protocol that establishes a provably secure proof of stake (PoS) system, the first of its kind to be rigorously analysed for security. Originating from foundational academic research and formally introduced in 2017, Ouroboros overcomes the energy-intensive limitations of Proof of Work (PoW) protocols. It underpins the Cardano blockchain, utilising a unique epoch system where a set of randomly chosen leaders is responsible for block production during each epoch. The protocol is based on strong cryptographic principles, delivers high transaction throughput, and ensures long-term sustainability without compromising decentralisation or security.