# Proof of Stake (PoS)

PoS is a newer, less energy-intensive, and thus more sustainable consensus mechanism than PoW. Through PoS consensus, holders of a blockchain asset can participate in securing and validating on-chain transactions by delegating their stake to a validator.

Launched in 2012, [Peercoin](https://www.peercoin.net/) was the first PoS project. [Cardano](https://docs.cardano.org/), [Polygon](https://polygon.technology/about)**,** and [Tezos](https://tezos.com/learn/what-is-tezos/) are three popular PoS blockchains. Ethereum has recently moved from PoW to PoS after a successful ‘Merge’.

It is important to note that unlike Ethereum’s version of PoS, however, Cardano’s PoS mechanism:

* Enables liquid staking (i.e. no lock-up) through which holders of Cardano native tokens can withdraw their stake or delegate it to another validator (stake pool) at any time.
* Requires a small initial amount of 2.17 ada to start staking
* Has no slashing feature that risks unfairly punishing delegators for staking to nodes that do not operate as intended.

[Ouroboros](https://www.essentialcardano.io/glossary/ouroboros) is Cardano’s PoS consensus protocol and was the first provably secure PoS protocol. In other words, Ouroboros offers *mathematically verifiable* security against attackers. The protocol is guaranteed to be secure, as long as 51% of the stake is held by honest participants. According to [Google scholar](https://scholar.google.com/scholar?hl=en\&as_sdt=0%2C5\&q=ouroboros\&btnG=), the original paper has been academically cited more than 1400 times, and variants of the protocol are used on other PoS chains.