The Beacon Chain is the proof-of-stake consensus layer of Ethereum. It launched on 1 December 2020 as a separate blockchain running alongside the original proof-of-work Ethereum network, with validators staking ether to propose and attest to blocks. On 15 September 2022, in an upgrade known as the Merge, the original chain's execution layer was joined to the Beacon Chain, and Ethereum switched entirely from mining to proof of stake.
Today the Beacon Chain is no longer a separate network but the part of Ethereum that coordinates validators, chooses who proposes each block and decides which blocks are final. Ethereum documentation now usually calls it the consensus layer, while the part that runs transactions and smart contracts is the execution layer. The term should not be confused with the BNB Beacon Chain, the renamed Binance Chain, which was a different network and has since been shut down.
Beacon Chain in plain terms
Think of Ethereum as a train. Before 2022, the engine pulling it was proof-of-work mining, which burned large amounts of electricity. Engineers built a new, much more efficient engine, the Beacon Chain, and ran it on a parallel track for nearly two years to make sure it worked. Then, while the train kept moving, they coupled the carriages to the new engine and detached the old one.
Passengers barely noticed: account balances, contracts and history stayed the same. What changed was who keeps the train on time. Instead of miners competing with computers, validators who lock up ether take turns proposing blocks and checking each other's work, and lose some of their deposit if they cheat.
History
Ethereum's founders planned a move to proof of stake from the network's early years. Research on designs called Casper and sharding led to a staged roadmap. Key milestones were:
- Deposit contract. In November 2020 a contract on the original chain began accepting deposits of 32 ETH per validator; once enough ether was deposited, the Beacon Chain launched.
- Altair, 2021. The first Beacon Chain upgrade added light-client support and adjusted rewards and penalties.
- The Merge, 2022. Carried out without a contentious chain split, it joined the execution layer to the Beacon Chain, ending mining and cutting Ethereum's energy use by more than 99%.
- Shapella, 2023. Validators could withdraw staked ether and rewards for the first time.
- Later upgrades. Dencun in 2024 added cheaper data "blobs" for layer 2 rollups, and Pectra in 2025 raised the maximum effective balance per validator from 32 ETH to 2,048 ETH, allowing larger operators to consolidate.
How the consensus layer works
Time on the Beacon Chain is divided into slots of 12 seconds and epochs of 32 slots, about 6.4 minutes. In each slot one validator is chosen at random to propose a block, and committees of other validators attest to which block they consider the head of the chain. Ethereum's consensus protocol, called Gasper, combines a fork-choice rule with a finality gadget: when validators holding two-thirds of staked ether attest to a checkpoint across two epochs, the blocks behind it become final and can only be reversed by destroying a large amount of stake. Validators earn rewards for timely duties and lose small amounts when offline. Signing contradictory messages leads to slashing, in which part of the stake is destroyed and the validator is removed. Ether is staked directly, through staking pools, or through liquid staking protocols that issue a tradable token in return. Ether itself is described in the entry Ethereum (ETH).
Role after the Merge
Every Ethereum node now runs two pieces of software: an execution client and a consensus client, which connect through a standard interface. The consensus client follows the Beacon Chain, while the execution client processes transactions, runs smart contracts and maintains the state of the Ethereum Virtual Machine. Having several independent client teams on each side is meant to avoid a single bug taking down the network. Block production has also been shaped by proposer-builder separation through external software, in which specialised builders assemble blocks and proposers choose the most profitable one.
Criticism and open issues
Critics of proof of stake argue that it favours those who already hold large amounts of ether and that staking has become concentrated in a few providers, including large exchanges and liquid staking protocols, raising concerns about decentralization and censorship. The dominance of a small number of block builders is another concern. Finality has occasionally been delayed when bugs in client software caused many validators to fall behind, as happened briefly in May 2023, though the chain kept producing blocks. Researchers continue to work on shorter finality times, lighter validator requirements and changes to the staking model as part of Ethereum's longer-term roadmap. The wider network is described in Ethereum Blockchain.