What is consensus in a blockchain?
Consensus in plain words
Many participants in a network each keep a copy of the blockchain, and any of them can send in new transfers. Yet all the copies have to match, holding the same records in the same order. The consensus rules are written into the software that the participants run themselves, so each participant checks and applies those rules on its own. They are also called a consensus mechanism.
Picture neighbors in an apartment building who keep a notebook of shared expenses, each with their own copy. Now and then two of them send in entries at the same moment, or someone tries to write down the same payment twice. To keep the notebooks from drifting apart, the neighbors agreed on a rule in advance. One of them at a time makes the entries, the others check and sign, and a line counts as accepted once two thirds or more of the neighbors have signed it. A consensus mechanism works the same way, except that the ones agreeing are many computers that do not know each other, and one of them may be a cheat.
What problem consensus solves
A recipient has no way to check alone whether the sender already spent those coins, and such a check usually requires a trusted central party1. In everyday life that central party is a bank. A blockchain has none, so the participants agree among themselves which of two transfers of the same coins came first and reject the other one. Trying to spend the same amount twice is called a double spend.
What happens if two blocks appear at the same time?
If two participants propose different blocks at the same moment, the network briefly has two branches, meaning two versions of the latest records. In Bitcoin the longest chain rule settles the dispute. Nodes, the computers that store the blockchain, treat as correct the branch with more computational work behind it, and as soon as one branch grows by another block, the remaining nodes switch to it1. This is why the most recent block can still be replaced, and why services wait for new blocks to pile up on top of a transfer.
When a transfer becomes final
A transfer is final when the network's rules no longer allow it to be reversed or rewritten. Each network reaches that point in its own way, and it decides when an exchange will credit your cryptocurrency.
- Bitcoin has no strictly final moment. Every new block added after yours makes reversing the transfer more expensive, and the chance of a reversal falls quickly1. Exchanges therefore credit bitcoin after several confirmations, that is, new blocks on top of the transfer, and each exchange sets its own number.where to check: the deposit rules on the exchange's website
- In Ethereum a block becomes final after validators vote on it. As of 24.10.2026 this takes about 15 minutes2.
- In Solana, since an upgrade in October 2026, a block is final after one or two rounds of voting by validators3.
- In the XRP Ledger, new versions of the records usually close every 3 to 5 seconds4, and a validated version counts as final5.
What consensus means for you
Consensus also sets the price of cheating a network. In computation-based networks an attacker needs most of the total computing power; in deposit-based ones, most of the deposit, which the attacker risks losing. The article miners and validators covers what such an attack can and cannot achieve.
Consensus protects the order of records in the network. Access to your cryptocurrency depends on your key, and if someone steals the key, no consensus rule will stop the thief. How to keep the key safe is explained in the article what is a private key. Nor will consensus bring back a mistaken transfer, since it records that transfer as reliably as a correct one.
What types of consensus mechanisms exist
Consensus mechanisms differ in what earns a participant the right to add a block and what that participant loses by cheating.
In Proof of Work, a block may be added by whoever first solves a hard puzzle by trying one guess after another. The weight of a vote here equals computing power, which Bitcoin's creator called the principle of "one-CPU-one-vote"1. Bitcoin works this way, and more about miners is in miners and validators.
In Proof of Stake, a participant earns its turn with a deposit of its own coins. The rules pick, in turn, the validator that will assemble the block, and the more coins a validator has on deposit, the more weight its vote carries. Ethereum works this way; it switched to this method on 15 September 2022, and afterwards the network's electricity use fell by roughly 99.95%6. Solana runs on deposits too, with voting rules of its own. In October 2026 those rules were updated so that transfers are confirmed faster3, and the hub on the Solana network explains in detail how they work.
The XRP Ledger network uses neither a computing race nor deposits. Transfers are agreed on by validator servers, and each server listens only to the servers it trusts. After a few rounds of comparing notes, they settle on a shared version of the records5. Validators are not paid for their work, because the server owners themselves need the network to run smoothly7. The coin of this network is called XRP.
How consensus differs in the Bitcoin, Ethereum, Solana and XRP Ledger networks
 Bitcoin |  Ethereum | Solana | XRP Ledger | |
|---|---|---|---|---|
| Does computation earn the right to a block? | yes | no | no | no |
| Does a deposit of coins give the right to add blocks? | no | yes | yes | no |
| Is there a reward for the work? | yes | yes | yes | no |
| Can a rule-breaker lose its deposit? | no | yes | no1 | no |
| Is a transfer final within seconds? | no | no | yes2 | yes |
Who changes the consensus rules
The network's developers write the consensus rules, and new rules take effect once participants install the new version of the software. Holders usually have nothing to do, as was the case with Ethereum's switch to deposits and with the Solana upgrade3. If the new rules are incompatible with the old ones and some participants stay on the old version, the network can split in two, as the article hard fork explains.
More detail on where the problem came from and how finality works
The problem is older than blockchains. In 1982 Leslie Lamport, Robert Shostak and Marshall Pease described it as the Byzantine Generals Problem: generals must agree on a common plan even though some of them may be traitors11. Consensus solves it for an open network that anyone can join.
Ethereum's 2022 switch to deposits is known as The Merge. A block in Ethereum is final once validators holding at least two thirds of all deposited coins have voted for it. Reversing such a block would cost a rule-breaker at least a third of the total deposit12.
Since 21 October 2026, Solana validators have voted under the Alpenglow system, which replaced the earlier Tower BFT. Under it, finality comes after one round of voting if validators holding 80% of the deposit vote in favor straight away, and otherwise after a second round. Since this upgrade, the network's built-in clock, Proof of History, no longer sets the pace of blocks3.
